A simulation study of horizontal well performance in a mature cyclic steam injection project in California is presented in this paper. Decline of production rates was observed in the field. This decline forced the operator to look into strategies of infill drilling and recompletion of existing wells. Horizontal infill wells, recompleted vertical wells, and mixed strategies were considered as the alternatives for further development of the reservoir. In 1997 Al-Hadrami et al.(1) presented the results of a simulation study for this field, where horizontal well strategies have been proven more productive than vertical well recompletion strategies. In the presented simulation study, performance of a single horizontal infill well has been studied in detail. A model simulating a section of the reservoir was developed with a refined grid around the horizontal well. The model includes all the key features of the reservoir. Using the developed model, a number of scenarios of horizontal well production were simulated in the range of applicable parameters (well location, injection rate, schedule). Details and description of simulated scenarios are presented in the paper. Scenarios are compared on the basis of cumulative oil production. Results indicate strong dependence of the cumulative oil production on the well location with reference to Water Oil Contact (WOC). Effects of injection rate, and well and injection timing are also illustrated. All the presented strategics result in an increase in cumulative production.