A CFD model for modeling gas evolution and flow patterns in a direct methanol fuel cell (DMFC) is presented. The model is based on two-fluid model with a new method for estimating the gas content without empirical mass transfer coefficients. The new equation for the source term is derived using the equilibrium flash equation for multicomponent gas-liquid stream. The improved two-fluid model allows studying the effect of flow field geometry on gas evolution and fuel cell performance without empirical correlations. The simulations of different flow field geometries provide a good illustration of the capability of the CFD model. Simulation results and main conclusions qualitatively agreed with experimental observations for a transparent DMFC available in literature. The developed 3D CFD model includes all relevant phenomena and factors and it is valuable for gas management in a DMFC design. This is an abstract of a paper presented at the 2005 AIChE Annual Meeting and Fall Showcase (Cincinnati, OH 10/30/2005-11/4/2005).