Oil yields, lithology, and stratigraphy have been evaluated for 15 cored wells and two sampled wells representing 10 square miles of the Tipton Member of the Green River Formation near Green River, Wyo. The are evaluated is being used by the Bureau of Mines for experimental production of oil from the oil shale's in place. Lithology and oil yields were correlated to produce a stratigraphy diagram for the in situ study area, permitting precise designation of comparable section. Because of lateral uniformity of oil shale, oil yields from eight cores and two sets of drill fitting samples within a quarter section show the range of variation in average oil yield arising form experimental error. Variation in average oil yields from the seven cores representing the 10 square mile study are lies within the expected experimental error. No difference in oil shale richness across the study area is indicated.