On the linear approximation of mixture internal energies of departure

•Linear mixing rule for mixture internal energies of departure validated.•Comparisons are made to direct Monte Carlo simulation in the NPT ensemble.•Gas–oil, oil–oil and oil–water mixtures are considered.•Sensitivity analysis of aM and VM to uncertainty in UMD presented.

Direct Monte Carlo simulation of internal energies of departure for binary mixtures of geological interest are gathered and compared to those calculated using a linear mixing rule. Simulation results for gas–oil, oil–oil, and oil–water mixtures show that the linear mixing rule used in the Gibbs–Helmholtz Constrained (GHC) equation of state framework gives accurate approximations of binary mixture internal energies of departure. A flowchart for computing internal energies of departure using Monte Carlo simulation is included along with a sensitivity analysis for the GHC mixture energy parameter with respect to uncertainty in internal energies of departure.