1. A method of evaluating the performance of a plurality of oil wells which were established to produce from a common reservoir beneath the earth's surface, comprising: a) inputting information into a digital computer respecting the size/shape of the reservoir, the locations of the wells and the production/injection history of the wells; b) establishing a time interval and time steps within said time interval over which the performance of the wells will be evaluated; c) determining the total oil which is accessible to each said well in each time step in said time interval; d) determining an individual recovery factor for each well for each time step in said time interval, where said recovery factor is defined as the ratio of actual production from each well during said time step to total oil accessible to each said well; e) determining a composite overall recovery factor for each said well over the time interval.