TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractUncertainties arise while interpreting transient tests in horizontal wells. This study presents a hybrid approach in that both analytic and numeric models are used to circumvent most of the problems associated with the conventional analytic interpretation.This novel approach entails multiple steps. Initially, reservoir parameters are estimated by identifying as many flow regimes as possible using the analytic method. Thereafter, a numeric simulation model is built using a coupled wellbore-reservoir simulator. Herein, we seek to match the wellbore flow profile data, collected by production logs (PL), by adjusting local permeability and skin. This PLmatched model then allows rate calculation during the transient-test periods, using measured bottomhole pressure as the inner-boundary condition. Finally, the computed rate is convolved with pressure to interpret the drawdown data for seeking reconciliation with buildup interpretation.We present two field examples to illustrate the application of the notion presented here. Complications arise while interpreting flow and buildup tests using conventional tools, because of complex well trajectories penetrating this heterogeneous carbonate reservoir. Results show that reservoir anisotropy (k v /k h ) is a very sensitive parameter and is therefore well determined. The history-matched model was quite successful in predicting the water cut behavior over 18 months in one of the wells.