A simple model is presented that accounts for the effects of temperature, pressure, and externally supplied gas flow rate on the kinetics of oil evolution during oil shale pyrolysis. The primary transport mechanism for generated oil from retorting oil shale particles is, by far, vaporization in co-generated gases. The simple model is based on the concept that an equivalent volatility of the oil must be achieved in order to attain the same extent of oil evolution from the particle. Oil generated at lower temperature (hence, lower volatility) must undergo additional coking and cracking reactions to reach equivalent volatility, and that effect can be modeled by adding a simple term to the effective activation energy. This simple approach explains Much of the compensation effect observed in the literature between apparent activation energies and frequency factors derived under different pyrolysis conditions. A similar approach can model the effect of pressure on oil evolution. The effect of pyrolysis temperature on volatility is reduced in the presence of An external purge gas, and the effect of the additional temperature term can be reduced by dividing it by a dimensionless flow rate. Sample correlations are presented between oil yield and various product quantities and qualities, as Well as inter relationships among various product properties for the Green River oil shale. Although these effects have been modeled more rigorously by coupling chemical kinetic models to vapor liquid equilibrium models, the current model is simpler to incorporate into integrated process models. Generalization to other rocks is discussed briefly.