Wagering game having a ramping bonus feature

Abstract

A gaming machine for conducting a wagering game includes a wager-input device for receiving a wager from a player to play a wagering game having a basic game and a standard bonus game. In response to the wager being at least as large as a threshold amount, a hidden trigger for randomly triggering the bonus game is enabled. A display displays symbols during the basic game. The symbols indicate a randomly selected outcome selected from a plurality of outcomes in response to the wager. The plurality of outcomes include at least one bonus-game-triggering outcome for triggering the bonus game. A probability of randomly triggering the bonus game via the hidden trigger is related to an amount of the wager.

Description

RELATED APPLICATIONS

This application is related to and claims priority to U.S. Provisional Patent Application Serial No. 60/666,915 filed Mar. 31, 2005, titled “Wagering Game Having A Ramping Bonus Feature,” which is incorporated herein in its entirety.

COPYRIGHT

A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.

FIELD OF THE INVENTION

The present invention relates generally to gaming machines, and methods for playing wagering games, and more particularly, to a gaming machine for implementing a wagering game having a ramping bonus game trigger that awards bonus game play based on the amount of the player's wager.

BACKGROUND OF THE INVENTION

Gaming machines, such as slot machines, video poker machines and the like, have been a cornerstone of the gaming industry for several years. Generally, the popularity of such machines with players is dependent on the likelihood (or perceived likelihood) of winning money at the machine and the intrinsic entertainment value of the machine relative to other available gaming options. Where the available gaming options include a number of competing machines and the expectation of winning at each machine is roughly the same (or believed to be the same), players are likely to be attracted to the most entertaining and exciting machines. Shrewd operators consequently strive to employ the most entertaining and exciting machines, features, and enhancements available because such machines attract frequent play and hence increase profitability to the operator. Therefore, there is a continuing need for gaming machine manufacturers to continuously develop new games and improved gaming enhancements that will attract frequent play through enhanced entertainment value to the player.

One concept that has been successfully employed to enhance the entertainment value of a game is the concept of a “secondary” or “bonus” game that may be played in conjunction with a “basic” game. The bonus game may comprise any type of game, either similar to or completely different from the basic game, which is entered upon the occurrence of a selected event or outcome in the basic game. Generally, bonus games provide a greater expectation of winning than the basic game and may also be accompanied with more attractive or unusual video displays and/or audio. Bonus games may additionally award players with “progressive jackpot” awards that are funded, at least in part, by a percentage of coin-in from the gaming machine or a plurality of participating gaming machines. Because the bonus game concept offers tremendous advantages in player appeal and excitement relative to other known games, and because such games are attractive to both players and operators, there is a continuing need to develop gaming machines with new types of bonus games to satisfy the demands of players and operators.

Operators of gaming machines strive to keep high worth players playing on their gaming machines. However, as more and more players go to a penny configuration game, operators have pulled the return percentage down to a relatively low amount, such as 86%. By doing so, players who would normally wager a $2-$3 bet often choose to forgo the machines having these low return percentages. A need therefore exists for providing players with a fair level of game play for their bet level. The present invention is directed to satisfying this and other needs.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a gaming machine for conducting a wagering game includes a wager-input device for receiving a wager from a player to play a wagering game having a basic game and a bonus game. In response to the wager being at least as large as a threshold amount, a hidden trigger for randomly triggering the bonus game is enabled. A display displays symbols during the basic game. The symbols indicate a randomly selected outcome selected from a plurality of outcomes in response to the wager. The plurality of outcomes include at least one bonus-game-triggering outcome for triggering the bonus game. A probability of randomly triggering the bonus game via the hidden trigger is related to an amount of the wager.

According to another aspect of the invention, a method of conducting a wagering game on a gaming machine comprises receiving a wager from a player to player the wagering game. The wagering game has a basic game and a bonus game. A game outcome is randomly selected from a plurality of outcomes in response to the wager. In response to the wager being at least as large as a threshold amount, a hidden trigger is enabled that randomly triggers the bonus game. A probability of randomly triggering the bonus game is related to an amount of the wager. The game outcome for the wagering game is displayed as symbols indicating a randomly selected outcome selected from a plurality of outcomes. The plurality of outcomes includes at least one bonus-game-triggering outcome for triggering the bonus game. The bonus game is activated if the bonus-game-triggering event is achieved or if the hidden trigger randomly triggers the bonus game.

According to yet another aspect of the invention, a computer readable storage medium is encoded with instructions for directing a gaming device to perform the above method.

According to an additional aspect of the invention, a gaming system is provided for playing a wagering game having a basic game and a bonus game. The gaming system has at least one display and a controller coupled to the display. The controller is programmed to initiate the wagering game in response to detection of a wager from a player. A basic game of the wagering game displays symbols indicating a randomly selected outcome selected from a plurality of outcomes based on a first random-number generator event. The plurality of outcomes include at least one bonus-game-triggering outcome for triggering a bonus game. In response to the wager being at least as large as a threshold amount, a hidden trigger is enabled that randomly triggers the bonus game based on a second random-number generator event. A probability of triggering the bonus game by the alternative-bonus feature is related to an amount of the wager.

According to another aspect of the invention, a method of playing a wagering game having a basic game and a bonus game that is triggered by an outcome in the basic game comprises receiving from a player a first wager amount, a second wager amount, or a third wager amount for playing the wagering game. The third wager amount is larger than the second wager amount, and the second wager amount is larger than the first wager amount. The basic game is played in response to the first wager amount being received. In response to the second wager amount being received, the basic game is played and a random selection is independently conducted with a hidden trigger that randomly triggers the bonus game. The hidden trigger triggers the bonus game at a first probability. In response to the third wager amount being received, the basic game is played and the random selection is independently conducted with the hidden trigger. The hidden trigger triggers the bonus game at a second probability.

Additional aspects of the invention will be apparent to those of ordinary skill in the art in view of the detailed description of various embodiments, which is made with reference to the drawings, a brief description of which is provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a gaming machine embodying the present invention;

FIG. 2 is a block diagram of a control system suitable for operating the gaming machine;

FIG. 3 illustrates a video slot wagering game according to an embodiment of the invention;

FIG. 4 illustrates the video slot wagering game in which the player has achieved a bonus-triggering symbol combination according to an embodiment of the invention;

FIG. 5 illustrates the primary display when the controller has triggered the “Ramp Up” enabled bonus game according to an embodiment of the invention; and

FIG. 6 illustrates a bonus game according to an embodiment of the invention.

DETAILED DESCRIPTION

While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiments illustrated.

Referring to FIG. 1, a gaming machine 10 is used in gaming establishments such as casinos. With regard to the present invention, the gaming machine 10 may be any type of gaming machine and may have varying structures and methods of operation. For example, the gaming machine 10 may be an electromechanical gaming machine configured to play mechanical slots, or it may be an electronic gaming machine configured to play a video casino game, such as blackjack, slots, keno, poker, blackjack, roulette, etc.

The gaming machine 10 comprises a housing 12 and includes input devices, including a value input device 18 and a player input device 24. For output the gaming machine 10 includes a primary display 14 for displaying information about the basic wagering game. The primary display 14 can also display information about a bonus wagering game and a progressive wagering game. The gaming machine 10 may also include a secondary display 16 for displaying game events, game outcomes, and/or signage information. While these typical components found in the gaming machine 10 are described below, it should be understood that numerous other elements may exist and may be used in any number of combinations to create various forms of a gaming machine 10.

The value input device 18 may be provided in many forms, individually or in combination, and is preferably located on the front of the housing 12. The value input device 18 receives currency and/or credits that are inserted by a player. The value input device 18 may include a coin acceptor 20 for receiving coin currency (see FIG. 1). Alternatively, or in addition, the value input device 18 may include a bill acceptor 22 for receiving paper currency. Furthermore, the value input device 18 may include a ticket reader, or barcode scanner, for reading information stored on a credit ticket, a card, or other tangible portable credit storage device. The credit ticket or card may also authorize access to a central account, which can transfer money to the gaming machine 10.

The player input device 24 comprises a plurality of push buttons 26 on a button panel for operating the gaming machine 10. In addition, or alternatively, the player input device 24 may comprise a touch screen 28 mounted by adhesive, tape, or the like over the primary display 14 and/or secondary display 16. The touch screen 28 contains soft touch keys 30 denoted by graphics on the underlying primary display 14 and used to operate the gaming machine 10. The touch screen 28 provides players with an alternative method of input. A player enables a desired function either by touching the touch screen 28 at an appropriate touch key 30 or by pressing an appropriate push button 26 on the button panel. The touch keys 30 may be used to implement the same functions as push buttons 26. Alternatively, the push buttons 26 may provide inputs for one aspect of the operating the game, while the touch keys 30 may allow for input needed for another aspect of the game.

The various components of the gaming machine 10 may be connected directly to, or contained within, the housing 12, as seen in FIG. 1, or may be located outboard of the housing 12 and connected to the housing 12 via a variety of different wired or wireless connection methods. Thus, the gaming machine 10 comprises these components whether housed in the housing 12, or outboard of the housing 12 and connected remotely.

The operation of the basic wagering game is displayed to the player on the primary display 14. The primary display 14 can also display the bonus game associated with the basic wagering game. The primary display 14 may take the form of a cathode ray tube (CRT), a high resolution LCD, a plasma display, an LED, or any other type of display suitable for use in the gaming machine 10. As shown, the primary display 14 includes the touch screen 28 overlaying the entire monitor (or a portion thereof) to allow players to make game-related selections. Alternatively, the primary display 14 of the gaming machine 10 may include a number of mechanical reels to display the outcome in visual associated to at least one payline 32. In the illustrated embodiment, the gaming machine 10 is an “upright” version in which the primary display 14 is oriented vertically relative to the player. Alternatively, the gaming machine may be a “slant-top” version in which the primary display 14 is slanted at about a thirty-degree angle toward the player of the gaming machine 10.

A player begins play of the basic wagering game by making a wager via the value input device 18 of the gaming machine 10. A player can select play by using the player input device 24, via the buttons 26 or the touch screen keys 30. The basic game consists of a plurality of symbols arranged in an array, and includes at least one payline 32 that indicates one or more outcomes of the basic game. Such outcomes are randomly selected in response to the wagering input by the player. At least one of the plurality of randomly-selected outcomes may be a start-bonus outcome, which can include any variations of symbols or symbol combinations triggering a bonus game.

In some embodiments, the gaming machine 10 may also include a player information reader 52 that allows for identification of a player by reading a card with information indicating his or her true identity. The player information reader 52 is shown in FIG. 1 as a card reader, but may take on many forms including a ticket reader, bar code scanner, RFID transceiver or computer readable storage medium interface. Currently, identification is generally used by casinos for rewarding certain players with complimentary services or special offers. For example, a player may be enrolled in the gaming establishment's loyalty club and may be awarded certain complimentary services as that player collects points in his or her player-tracking account. The player inserts his or her card into the player information reader 52, which allows the casino's computers to register that player's wagering at the gaming machine 10. The gaming machine 10 may use the secondary display 16 or other dedicated player-tracking display for providing the player with information about his or her account or other player-specific information. Also, in some embodiments, the information reader 52 may be used to restore game assets that the player achieved and saved during a previous game session.

Turning now to FIG. 2, the various components of the gaming machine 10 are controlled by a central processing unit (CPU) 34, also referred to herein as a controller or processor (such as a microcontroller or microprocessor). To provide gaming functions, the controller 34 executes one or more game programs stored in a computer readable storage medium, in the form of memory 36. The controller 34 performs the random selection (using a random number generator (RNG)) of an outcome from the plurality of possible outcomes of the wagering game. Alternatively, the random event may be determined at a remote controller. The remote controller may use either an RNG or pooling scheme for its central determination of a game outcome. It should be appreciated that the controller 34 may include one or more microprocessors, including but not limited to a master processor, a slave processor, and a secondary or parallel processor.

The controller 34 is also coupled to the system memory 36 and a money/credit detector 38. The system memory 36 may comprise a volatile memory (e.g., a random-access memory (RAM)) and a non-volatile memory (e.g., an EEPROM). The system memory 36 may include multiple RAM and multiple program memories. The money/credit detector 38 signals the processor that money and/or credits have been input via the value input device 18. Preferably, these components are located within the housing 12 of the gaming machine 10. However, as explained above, these components may be located outboard of the housing 12 and connected to the remainder of the components of the gaming machine 10 via a variety of different wired or wireless connection methods.

As seen in FIG. 2, the controller 34 is also connected to, and controls, the primary display 14, the player input device 24, and a payoff mechanism 40. The payoff mechanism 40 is operable in response to instructions from the controller 34 to award a payoff to the player in response to certain winning outcomes that might occur in the basic game or the bonus game(s). The payoff may be provided in the form of points, bills, tickets, coupons, cards, etc. For example, in FIG. 1, the payoff mechanism 40 includes both a ticket printer 42 and a coin outlet 44. However, any of a variety of payoff mechanisms 40 well known in the art may be implemented, including cards, coins, tickets, smartcards, cash, etc. The payoff amounts distributed by the payoff mechanism 40 are determined by one or more pay tables stored in the system memory 36.

Communications between the controller 34 and both the peripheral components of the gaming machine 10 and external systems 50 occur through input/output (I/O) circuits 46, 48. More specifically, the controller 34 controls and receives inputs from the peripheral components of the gaming machine 10 through the input/output circuits 46. Further, the controller 34 communicates with the external systems 50 via the I/O circuits 48 and a communication path (e.g., serial, parallel, IR, RC, 10bT, etc.). The external systems 50 may include a gaming network, other gaming machines, a gaming server, communications hardware, or a variety of other interfaced systems or components. Although the I/O circuits 46, 48 may be shown as a single block, it should be appreciated that each of the I/O circuits 46, 48 may include a number of different types of I/O circuits.

Controller 34, as used herein, comprises any combination of hardware, software, and/or firmware that may be disposed or resident inside and/or outside of the gaming machine 10 that may communicate with and/or control the transfer of data between the gaming machine 10 and a bus, another computer, processor, or device and/or a service and/or a network. The controller 34 may comprise one or more controllers or processors. In FIG. 2, the controller 34 in the gaming machine 10 is depicted as comprising a CPU, but the controller 34 may alternatively comprise a CPU in combination with other components, such as the I/O circuits 46, 48 and the system memory 36.

Turning now to FIG. 3, a video slot wagering game is displayed on the primary display 14. The video slot wagering game includes five reels, 300, 305, 310, 315, and 320, each of which have three visible symbols. In other embodiments, more or fewer than five reels may be utilized, and more or fewer than three symbols are visible on each reel. This video slot wagering game allows a wager as low as one cent/credit, and has 20 lines on which the player may place a wager. In other embodiments, the minimum wager may be larger than one credit such as, e.g., 5 or 25 credits. As illustrated in FIG. 3, the player has wagered 5 credits on each of the 20 lines, for a total wager of 100 credits. In other embodiments, more or fewer than 20 lines may be used.

This video slot wagering game provides a bonus game when a certain bonus-triggering symbol combination is displayed on the reels. In some embodiments, there are multiple different symbol combinations that trigger the bonus game. In other embodiments, there is only a single symbol combination that triggers the bonus game.

FIG. 4 illustrates the video slot wagering game in which the player has achieved a bonus-triggering symbol combination according to an embodiment of the invention. This video slot wagering game, entitled “The Jade Monkey,” has a bonus game that can be triggered by achieving a scattered symbol combination of three jade monkey symbols 400. A scattered symbol combination is a combination of symbols across the reels that do not have to be located on a single active payline in order to form a winning combination. As shown, the player did receive a combination of three jade monkey symbols 400—one as the middle symbol of the first reel 300, one as the top symbol of the second reel 305, and one as the middle symbol on the fifth reel 320. Accordingly, the bonus game will be triggered based on this symbol combination.

In addition to the standard method of triggering bonus game play (i.e., by achieving a bonus game-triggering symbol combination), an additional bonus game trigger is provided to award bonus game play independent of the symbol combinations on the reels 300, 305, 310, 315, and 320. Specifically, the player may be awarded a bonus game based on a hidden trigger (i.e., a trigger not displayed to the player) regardless of the displayed symbols. As used in the illustrated embodiment, this type of bonus game is referred to herein as a “Ramp Up” enabled bonus game that is triggered based upon the amount of the player's wager. Increasing the player's wager “ramps up” the probability of triggering the “Ramp Up” enabled bonus game. That is, the larger the player's wager, the easier it is for the player to trigger the “Ramp Up” enabled bonus game. Accordingly, use of the “Ramp Up” enabled bonus game encourages the player to wager increasing amounts. In some embodiments, the “Ramp Up” enabled bonus game is available only if the player has wagered more than one credit per line. In other embodiments, the “Ramp Up” enabled bonus game is available even in the event that the player has wagered as little as a single credit per line.

The trigger for the “Ramp Up” enabled bonus game is implemented in a “hidden” fashion—the triggering of the bonus in this manner is independent of the symbols shown on the display screen. The player only becomes aware that he/she has triggered this bonus once the gaming machine 10 notifies the player. Accordingly, as discussed above, there is no visible trigger for this “Ramp Up” enabled bonus game.

In one embodiment, the “Ramp Up” enabled bonus game is the same as the standard bonus game (i.e., triggering the “Ramp Up” enabled bonus game sends the player to the standard bonus game). Accordingly, the player has the chance to play the standard bonus game if either the standard bonus triggering symbol combination has been achieved or the “Ramp Up” enabled bonus game is triggered. In other embodiments, the “Ramp Up” enabled bonus game is different from the standard bonus game. The “Ramp Up” enabled bonus game may be a non-progressive bonus game.

FIG. 5 illustrates the primary display 14 when the controller 34 has triggered the “Ramp Up” enabled bonus game according to an embodiment of the invention. In the event that the “Ramp Up” enabled bonus game is triggered, this “Ramp Up Bonus” symbol 500 would be displayed. The “Ramp Up Bonus” symbol 500 may be displayed before, after, or while the reels 300, 305, 310, 315, and 320 are spinning. The player would then have the opportunity to play the “Ramp Up” enabled bonus game. If the player achieves both a bonus-triggering combination and triggers the “Ramp Up” enabled bonus game simultaneously, then the player would initially play the bonus game triggered by the bonus-triggering combination and then play the “Ramp Up” enabled bonus game. Alternatively, the player may play a single bonus game when the bonus-triggering combination and the “Ramp Up” enabled bonus game are achieved simultaneously, and the results of the bonus game are multiplied by a factor such as 2 or 3. Accordingly, in either alternative, the player is awarded an enhanced bonus.

As discussed above, an aspect of the invention is that the player's chances of triggering the “Ramp Up” enabled bonus game increase based on the amount of the player's wager. Table 1 below illustrates the player's odds of achieving the various bonuses and the total return percentage in the bonus game, based on the amount of the player's wager. As shown, for all wagers the odds of achieving the bonus-triggering combination (e.g., the three jade monkey symbols 400 in FIG. 4) are 1 in 120 and the average return in the bonus is 32 times the wager. In this embodiment, if the player has wagered a single credit per line, then the player is ineligible for the “Ramp Up” enabled bonus game. Accordingly, if a single credit per line is wagered, the player's total return percentage in the bonus is 26.67% (i.e., the odds of being awarded the bonus times the average return in the bonus).

If the player has wagered 2 credits per line, the player is eligible for the “Ramp Up” enabled bonus game. The odds of triggering the “Ramp Up” enabled bonus game are 1 in 4680. Accordingly, the overall odds of being awarded the bonus game by either achieving the bonus-triggering combination or triggering the “Ramp Up” enabled bonus game are 1:117, and the total return percentage in the bonus is 27.35% when 2 credits per line are wagered. The odds steadily increase with each credit per line wagered. If 3 credits per line are wagered, the player's odds of triggering the “Ramp Up” enabled bonus game are 1 in 1680, the overall odds of being awarded a bonus are 1 in 112, and the total return percentage in the bonus game is 28.57%. In other words, the expected value of the bonus game increases based on the number of credits wagered per line, thereby providing an incentive for wagering more credits per line.

As shown in Table 1, the total return percentage for a wager of 2 credits per line is 0.78% (i.e., 27.35%-26.67%) greater than the total return percentage when one 1 credit per line is wagered. Accordingly, the total return percentage “ramps up” or increases based on the amount of credits wagered per line. If 3 credits per line are wagered, the ramp up in the return percentage from 1 to 3 credits per line is 1.90% (i.e., 28.57%-26.67%) and the ramp up from 2 to 3 credits is 1.22% (i.e., 28.57%-27.35%). If 4 credits per line are wagered, the ramp up in the return percentage from 1 to 4 credits per line is 3.24% (i.e., 29.91%-26.67%) and the ramp up from 3 to 4 credits is 1.34% (i.e., 29.91%-28.57%). If 5 credits per line are wagered, the ramp up in the return percentage from 1 to 5 credits per line is 4.40% (i.e., 31.07%-26.67%) and the ramp up from 4 to 5 credits is 1.16% (i.e., 31.07%-29.91%).

TABLE 1
Odds of achieving bonus game when the “Ramp Up”
enabled bonus game is implemented
	Odds of	Odds of
	achieving	being
	awarded	“Ramp	Overall
Amount of	bonus-	Up”	odds of	Average	Total
credits	triggering	enabled	being	return	return
wagered	symbol	bonus	award	in	percentage
per line	combination	game	the bonus	bonus	in bonus
1	1:120	0	1:120	32* Wager	26.67%
2	1:120	1:4680	1:117	32* Wager	27.35%
3	1:120	1:1680	1:112	32* Wager	28.57%
4	1:120	1:987	1:107	32* Wager	29.91%
5	1:120	1:727	1:105	32* Wager	31.07%

Table 1 shows the various odds for a wager of up to 5 credits merely for illustrative purposes. It should be appreciated that in some embodiments, the player's odds increase up until the maximum wager possible on the gaming machine 10 has been made (e.g., 100 credits). Also, the displayed odds are merely exemplary. Any suitable odds and average bonus payouts during bonus game play may be implemented.

FIG. 6 illustrates a bonus game according to an embodiment of the invention. As discussed above, this bonus game may be shown to the player either upon triggering the “Ramp Up” enabled bonus game or achieving a bonus-triggering symbol combination. In this bonus game, the player is shown an array of five columns 600, 605, 610, 615, and 620 and four rows 625, 630, 635, and 640 of player-selectable symbols 645 on the primary display 14. Each of these player-selectable symbols 645 mask a bonus award such as free spins, bonus payouts, etc. The player has the opportunity to select three of the player-selectable symbols 645 and reveal the masked bonus awards. In other embodiments, the player is allowed to continue selecting the player-selectable elements 645 until a bonus-game-ending symbol is selected, at which point the bonus game ends. The invention is not limited to this particular bonus game, and it should be appreciated that any number of different bonus games are suitable for use with the invention. In other embodiments, the “Ramp Up” enabled bonus game is a different bonus game than the standard bonus game triggered by achieving a bonus-triggering symbol combination.

The “Ramp Up” enabled bonus game rewards players betting above a minimum threshold wager (e.g., 1 credit) without alienating the single-credit players. The method of achieving the “Ramp Up” enabled bonus game can be completely hidden to the player and does not interfere with the basic game. It may therefore be added to a range of wagering games without additional art or reprogramming of the base games. This feature presents an exciting reward to players and increases loyalty to the wagering game.

As discussed above, the bonus game may be triggered by either a bonus-triggering symbol combination or a hidden trigger wherein the probability of achieving the hidden trigger is proportional to the amount of a player's wager (i.e., the higher the wager, the greater the probability of achieving the hidden trigger). Accordingly, the bonus game may be triggered by two unrelated events. As such, each of these events is awarded based on one or more random-number generator events.

Each of these embodiments and obvious variations thereof is contemplated as falling within the spirit and scope of the claimed invention, which is set forth in the following claims.

Claims

1. A gaming machine comprising:

a wager-input device for receiving a wager from a player to play a wagering game having a basic game and a bonus game, wherein in response to the wager being at least as large as a threshold amount, a hidden trigger for randomly triggering the bonus game is enabled;

a display for displaying symbols during the basic game, the symbols indicating a randomly selected outcome selected from a plurality of outcomes in response to the wager, the plurality of outcomes including at least one bonus-game-triggering outcome for triggering the bonus game; and

wherein a probability of randomly triggering the bonus game via the hidden trigger is related to an amount of the wager.

2. The gaming machine of claim 1, wherein in response to the at least one bonus-game-triggering outcome being achieved and the hidden trigger triggering the bonus game on the same wager, an enhanced bonus is awarded to the player.

3. The gaming machine of claim 2, wherein the enhanced bonus is successive plays of the bonus game.

4. The gaming machine of claim 1, wherein the threshold amount is two credits per line.

5. The gaming machine of claim 1, wherein the probability of triggering the bonus game via the hidden trigger increases as the amount of the wager increases.

6. The gaming machine of claim 1, wherein the randomly-selected outcome is selected based on a first random-number generator event, and the hidden trigger randomly triggers the bonus game based on a second random-number generator event.

7. A method of conducting a wagering game on a gaming machine, the method comprising:

receiving a wager from a player to play the wagering game, the wagering game having a basic game and a bonus game;

randomly selecting a game outcome from a plurality of outcomes in response to the wager;

enabling, in response to the wager being at least as large as a threshold amount, a hidden trigger for randomly triggering the bonus game, a probability of randomly triggering the bonus game via the hidden trigger being related to an amount of the wager;

displaying the game outcome for the wagering game as symbols indicating a randomly selected outcome selected from a plurality of outcomes, wherein the plurality of outcomes includes at least one bonus-game-triggering outcome for triggering the bonus game; and

activating the bonus game if the bonus-game-triggering event is achieved or if the hidden trigger randomly triggers the bonus game.

8. The method of claim 7, further including awarding an enhanced bonus to the player in response to the at least one bonus-game-triggering outcome being achieved and the hidden trigger triggering the bonus game on the same wager.

9. The method of claim 8, wherein the enhanced bonus is successive plays of the bonus game.

10. The method of claim 7, wherein the threshold amount is two credits per line.

11. The method of claim 7, wherein the probability of triggering the bonus game via the hidden trigger increases as the amount of the wager increases.

12. The method of claim 7, wherein the randomly selecting of the game outcome is based on a first random-number generator event, and the hidden trigger triggers the bonus game based on a second random-number generator event.

13. A computer readable storage medium encoded with instructions for directing a gaming device to perform the method of claim 7.

14. A gaming system for playing a wagering game having a basic game have a standard bonus game, comprising:

at least one display; and

a controller coupled to the display and programmed to initiate the wagering game in response to detection of a wager from a player, wherein a basic game of the wagering game displays symbols indicating a randomly selected outcome selected from a plurality of outcomes based on a first random-number generator event, the plurality of outcomes including at least one bonus-game-triggering outcome for triggering a bonus game; and enabling, in response to the wager being at least as large as a threshold amount, a hidden trigger to randomly trigger the bonus game based on a second random-number generator event, a probability of triggering the bonus game by the hidden trigger being related to an amount of the wager.

15. The gaming system of claim 14, wherein the display and the controller are both located within a gaming terminal.

16. The gaming system of claim 14, wherein the display is located within a gaming terminal and the controller is located outside of the gaming terminal.

17. The gaming system of claim 14, wherein the probability of triggering the bonus game via the hidden trigger increases as the amount of the wager increases.

18. The gaming system of claim 14, wherein in response to the at least one bonus-game-triggering outcome being achieved and the hidden trigger triggering the bonus game on the same wager, an enhanced bonus is awarded to the player.

19. A method of playing a wagering game having a basic game and a bonus game that is triggered by an outcome in the basic game, comprising:

receiving from a player a first wager amount, a second wager amount, or a third wager amount for playing the wagering game, the third wager amount being larger than the second wager amount, and the second wager amount being larger than the first wager amount;

in response to the first wager amount being received, playing the basic game;

in response to the second wager amount being received, playing the basic game and independently conducting a random selection with a hidden trigger that triggers a free play of the bonus game, the hidden trigger awarding the bonus game at a first probability; and

in response to the third wager amount being received, playing the basic game and independently conducting the random selection with the hidden trigger, the hidden trigger awarding the bonus game at a second probability.

20. The method of claim 19, wherein the second probability is greater than the first probability.