On the basis of assumptions of ideal liquid mixture, ideal gas behavior, and gas-liquid equilibrium, a dynamic model of a system for saturation of a gas with liquid hydrocarbons was obtained. Comparing experimental data with simulation runs validated the results; a high degree of accuracy was obtained in the estimates of both volume of liquid and the rate of change of the composition of the liquid phase. A narrow distribution of boiling points determines an almost linear behavior due to strong similarities among the molecules in the liquid mixture; a wide distribution of boiling points gives the system very strong nonlinear characteristics. Regardless of the distribution of boiling points, the model presented predicts very accurately the volume change and composition profiles at any given time for any number of compounds in a mixture of hydrocarbons. An analysis of the structure of the model correlated the vapor pressure to the absolute value of the eigenvalues of the linear system. This analysis allowed us to infer information on the complexity of the molecular interactions in an apparently simple system of contact between a gas and a liquid.