Mutual diffusion coefficients for the CO2–CH4 system were measured from 293 to 370°K. These measurements extend the temperature range of the previously measured values by about 75°K. The experimental values of the diffusion coefficient are in excellent agreement with values derived from the composition dependence of the viscosity of CO2–CH4 mixtures provided the quantity A12* which appears in the relation between the two transport properties is evaluated using experimental quantities.