We demonstrate that the adsorption of ethane on an industrial activated carbon may be predicted quantitatively using molecular simulations of a two-center model of ethane and a pore size distribution for the micropores of the active carbon. The pore size distribution was determined from the adsorption of methane on the same carbon at a single temperature. No adjustable solid-fluid parameters were used. A less realistic spherical model of ethane was not adequate to predict ethane adsorption.