Large volumes of oil and gas are present in the Arabian-Iranian Basin; however, most petroleum-geological investigations here have concentrated on reservoirs and traps, and there have been few efforts to study potential source rocks. This paper evaluates possible source rocks within the Lower to Middle Cretaceous interval in Kuwait, which is one of the main oil-and gas-producing countries in this region. Samples of carbonates and shales from formations within the Thamama and Wasia Groups (Lower and Middle Cretaceous) were collected from five locations in Kuwait. These samples were studied using standard organic-geochemical methods (TOC and pyrolysis analysis, elemental analyses of kerogens, density separation, and petrographic analyses using transmitted and reflected light microscopy). Most of the kerogens in the studied samples fell between Types II and III. The TOC, kerogen type and maturity of the Sulaiy Formation and parts of the Minagish Formation(Lower Cretaceous) indicate that they supplied hydrocarbons to the reservoirs in Kuwait.