New shape factors are developed for bounded reservoirs produced by wells operating at constant bottomhole pressure. The new shape factors should replace Dietz(1) shape factors (constant-rate shape factors) when calculating the productivity of wells producing at constant bottomhole pressure, thus obtaining a more reliable long-term production forecast. Although the constant-pressure and constant-rate shape factors are conceptually different, they are close in value for regular shapes (e.g., square reservoirs) with a well in the center. However, for irregular shapes and off-centered wells, the difference is significant. The use of constant-rate shape factors for predicting the performance of wells producing at constant bottomhole pressure results in over-estimation of well productivity.