We have determined the interaction second virial coefficients (B12) for the CO2 C2H6 system between 250 and 300K using a Burnett-isochoric apparatus. The technique follows a procedure suggested by Hall and Eubank (1973) and extended by Holste et al. (1980). Combined errors for B12 are within 1.2 cm3/mol. In addition, values for the binary interaction parameter k12 calculated from our B12 values show difinite temperature dependence.