Abstract The Cambay-Hazad(!) petroleum system in South Cambay basin, India, has original in-place oil and gas reserves of 395 million t. The system covers 9320 km2 encompassing 20 different oil and gas accumulations. Sedimentary rocks in this petroleum province range in age from Paleocene to Recent and were deposited in a Tertiary rift basin. Carbon isotopic and biological marker data indicate that the low sulfur, high API gravity oil originated from the lower-middle Eocene Cambay Shale source rock. Burial and thermal history reconstructions indicate that oil generation and migration occurred from Miocene (21 Ma) to Recent time. The overburden rocks are over 3 km thick and range in age from middle Eocene to Recent. The principal reservoir rocks are sandstone units of the Hazad and Ardol members of the Ankleshvar Formation. The essential elements of the petroleum system, consisting of the source, reservoir, seal, and overburden rocks, were deposited from early Eocene to Recent time and the critical processes of generation, migration, trap formation, and accumulation occurred from the Miocene to Recent. The mass of hydrocarbons generated by the Cambay Shale was calculated and compared to the estimated in-place oil and gas reserves to determine the efficiency of the petroleum system. On the basis of an average organic carbon content of 2.6%, a difference between the original and present- day hydrogen index of 28 mg HC/g TOC, and a 4057.5-km3 volume of mature source rock, it is estimated that about 7.61 x 1012 kg hydrocarbons were generated. Estimated in-place oil and gas reserves in accumulations within the system are 3.95 x 1011 kg hydrocarbons. These calculations indicate that about 5.2% of the generated hydrocarbons have accumulated in known fields.