1. A method for estimating minimum miscibility enrichment (MME) for an injectant used in gas flooding of a reservoir at a given operating pressure comprising: performing a plurality of slim tube simulations for the reservoir; determining minimum miscibility pressure (MMP) for each of a plurality of injected gases in the reservoir; creating a plot having a recovery factor (RF) vs. 1−(MMP−P)/MMP curve for each of the plurality of injected gases, wherein P is the operating pressure of the reservoir having at least one of the plurality of injected gases, wherein 1−(MMP−P)/MMP is a dimensionless pressure, wherein MMP is the minimum miscibility pressure of one of the plurality of injected gases from the determining step, and wherein the plot has a y-intercept and slope; combining all of the RF vs. 1−(MMP−P)/MMP curves for each of the plurality of injected gases to form one curve; obtaining a recovery factor equation RF=i+s(1−(MMP−P)/MMP) from the one curve, wherein i is the y-intercept and s is the slope; determining a value for i; determining a value for s; and calculating the recovery factor.