More than 1500 measurements of vitrinite reflectance (R°t), along with mathematical modeling and computing, have been used to map the uppermost Middle Jurassic sediments of the West Siberian basin according to thermal maturity (catagenesis). The thermal maturity varies within the grades PC3 to AC2. Sediments are the least mature along the margins of the basin, and the maturity grade increases progressively toward its central and northern parts (grades MC1-MC2). It reaches a maximum in the north (AC2), where the sediments which subsided to large depths became exposed to high temperatures and pressures. The maturity zones of Jurassic sediments in the West Siberian basin form a typical pattern of regional catagenesis.