ABSTRACT Organic geochemical and petrographic analyses were carried out on Paleozoic core samples to evaluate the source rocks in Kuwait. This is a pioneer study because most of the petroleum exploration targets the Mesozoic petroleum system. The samples were collected from four wells that penetrated the Permian Khuff Formation and the Carboniferous–lower Permian Unayzah Formation. Standard organic geochemical, vitrinite (Ro), and bitumen reflectance analyses were done on selected samples. Gas chromatography and gas chromatography–mass spectrometry as well as characterization of saturates, aromatics, and heteroatomic compounds (resin and asphaltene) were performed on two rock extracts. This was followed by carbon isotope analysis on the same extracts. The total organic carbon in the Khuff Formation ranges from 0.6 to 2.8 wt. % and from 0.8 to 3.7 wt. % in the Unayzah Formation. The highest total organic carbon values are in the northern fields. The petrography of the kerogen for both formations shows a mixture of algal-marine and terrestrial organic matter. The thermal maturity ranges from peak oil to overmature with elevated Ro (1.85%–2.57%). Gas chromatography on oil extracts from the Unayzah Formation indicates a marine source. Hopane biomarkers indicate a sapropelic–marine source rock. The pristane/phytane ratio and carbon isotope ratio indicate a dysoxic marine depositional environment. The oil extract shows a maturity level equivalent to the early to middle oil generation stage, which is lower than the kerogen maturity level. The results of bitumen reflectance show large variation in maturity level (0.5%–2% Ro) reflecting different migration time.