Abstract: A system and method are directed towards identifying advertisement keywords within a variety of content types, identifying similarity rankings of advertisements based on the keywords, and to the guiding of keyword purchases. In one embodiment, a search is performed based in part on defined selection criteria, and/or scheduling rules. Content that may include advertisements is processed to identify advertisement keywords. A similarity ranking of different advertisements based on keywords therein may be determined. The similarity rankings may be used, with keyword pricing data, to identify instances of keyword arbitrage, guide purchase of keywords, and to control traffic flow to and from advertisements to obtain a benefit from price differentials between what one keyword seller charges for a keyword and what a click buyer will, pay for traffic directed to advertisements with the same or related keyword.