This work presents a computer model which, when used in conjunction with a single well buildup test in a multiple well unsteady state oil reservoir, can give the true average reservoir pressure without prior knowledge of drainage area shapes. To sUbstantiate the accuracy of the model, test runs were made on regularly shaped reservoirs for which the solutions to the pressure function are known. The resulting comparisons were favorable. The model was then applied to irregularly shaped reservoirs for both equal and unequal rate cases. The mathematical basis for the model is shown along with the computational technique and instructions for use.