Abstract An analytical method for calculating an effective non-Darcy flow coefficient for a heterogeneous formation is presented. The method presented here can be used to calculate an effective non-Darcy flow coefficient for heterogeneous gridblocks in reservoir simulators. Based on this method, it is shown that the non-Darcy flow coefficient of a heterogeneous formation is larger than the non-Darcy flow coefficient of an equivalent homogenous formation. This result is confirmed using numerical simulations. Non-Darcy flow coefficients calculated from analysis of well test data from a gas condensate field show that non-Darcy flow obtained from well tests that are significantly larger than those predicted from experimental correlations. Permeability heterogeneity is, therefore, a very likely reason for differences in non-Darcy flow coefficients often seen between lab and field data. P. 215