The utilization of natural gas reserves with high carbon dioxide (co2) content poses an enrichment problem that requires separation. in addition, the proposed use of co2 for enhanced oil recovery creates further need to characterize the vapor-liquid equilibrium properties of ch4-co2 mixtures. cryogenic distillation has been proposed at low temperatures (< -50 oc) and pressures below 4 mpa, where the formation of solid co2 is possible. investigate the vapor-liquid equilibrium behavior for the ch4-co2 mixture for mixtures containing 10, 30, 50, 80 mol% ch4. one source for experimental data for the ch4-co2 system is mraw, hwang, and kobayashi, journal of chemical engineering data, vol. 23 (2), p. 135 (1978). compare the phase equilibrium boundaries by using the peng robinson and soave-redlick-kwang equations of states and also adjusting the binary interactions parameter (kij) so that the model predictions match as closely as possible to existing experimental data.