Abstract: We studied in this paper the shale oil basin located in the west of the USA filled with shallow marine sediments of K₂, of which the Formation A is the most popular shale oil production target in North America. The Formation consists of interbedded chalk and marl. Until now, eight shale oil fields have been discovered in the south of the basin, and are now in the development phase. We studied the production difference in the Z block of the basin and its relation with depth, thickness, Ro, TOC and brittleness through well data and seismic data. We found that the Ro has positive correlation with production, and fracture belt can help well increase in production. The best production wells are located in the area where the sediments are more brittle. Our data suggest that four geologic parameters, i.e. Ro, fracture belt, brittleness and structure complex, are critical for evaluation of production potentials. And according to the four parameters in the core area, the Z block could be divided four parts. The tier I is the best and the tier IV the worst.