The Gevar'am gray-black shales of Early Cretaceous age are present in the subsurface of the western coastal plain and offshore of Israel. The degree of maturation of the organic material in the shales, evaluated from the study of vitrinite reflectance measurements and the organochemical characteristics of 13 core extracts, appears to increase from immature in the east to the stage of thermal generation of oil in the west, in response to the increase in burial depth. The earliest time at which the physical conditions for oil generation were reached, as estimated from the geologic setting and the maturation stage of the organic material, seems to have been the Turonian-Senonian. Although, in the east, the maturation stage did not progress much after this period, westward a urther increase in the degree of maturation occurred in the Neogene as a result of the thicker accumulation of Neogene sediments. The organic material was derived mostly from terrestrial remains, although a marine microorganism contribution also is inferred.