An improved engine fuel control method which divides the liquid fuel into a plurality of components characterized by relative volatility. The mass and evaporation characteristics of each fuel volatility component are determined separately within the fuel puddle, with the overall puddle behavior being characterized as the sum of the behaviors of the individual volatility components. The method involves determining, for each engine cycle, the mass of fuel that will evaporate from the puddle, the mass of vapor required to achieve the desired air/fuel ratio for the engine cylinder, the fraction of the injected fuel that will vaporize, and the mass of fuel that needs to be injected in order to achieve the desired air/fuel ratio in the cylinder. Finally, the puddle mass is updated for the next intake event. In a preferred implementation, the liquid fuel is divided into first, second and third components respectively characterized by high, medium and low volatility, and the volatility is inferred based on a measure of the fired-to-motored cylinder pressure ratio.