Abstract: A method is disclosed for determining the minimum miscibility pressure of a three (3) or more component fluid system consisting of an in-place fluid and an injected fluid, such as a mixture of liquid and gaseous hydrocarbons and another gas, such as CO.sub.2 or nitrogen. For a given pressure, the concentration of the first fluid is varied until a multiphase fluid state is indicated. The coexisting equilibrium phase compositions are calculated to determine a tieline which is translated geometrically retaining the direction of its slope to estimate a new tieline which attempts to be coincident with the second fluid's composition. The method above is repeated utilizing an increased pressure if the new tieline is coincident with a second fluid's composition and utilizing a decreased pressure if a coincident tieline does not exist, until a boundary pressure is achieved which represents the minimum miscibility pressure.