An algorithm to determine the mass transfer rate from the surface of a pure liquid in conjunction with the volume of fluid (VOF) was developed. The algorithm determines the liquid/gas interface by using information of the volume fractions of individual phases in the flow field obtained from the VOF method. It then solves the species equation in the gas phase. It is assumed that the carrier gas at the liquid/gas interface is saturated with vapour. Four test cases were designed to evaluate the algorithm. Concentration profiles obtained from these test cases were compared with results from available analytical solutions. The algorithm was then implemented to determine vapour emission from a two-phase stratified flow inside an axisymmetric funnel representative of an automotive fuel filler pipe. © 2004 IMechE.