Potential source rocks in the Tarim Basin (NW China) include Cambrian-Lower Ordovician lagoonal carbonates and mudstones; Middle-Upper Ordovician platform carbonates; Carboniferous-Permian shallow-marine carbonates and mudstones; and Triassic-Jurassic continental deposits including coals and lacustrine mudstones. Our petrological observations show that the organic components in Cambrian-Ordovician deposits are mainly alginites and amorphinites with minor vitrinite-like macerals, zooclasts and solid bitumen (Type I organic matter). The organic carbon content of these rocks is 0.1-2% TOC (averaging 0.9%TOC in deeper-water facies) and they are mature to overmature in terms of oil generation. Organic macerals in Permian-Carboniferous source rocks are dominated by alginite with minor quantities of zooclasts and exinite derived from terrestrial higher plants (mainly Type H OM with minor Types I and III). TOC contents are 0.1-1%. These rocks are mature to highly-mature in terms of oil generation. Macerals in Jurassic-Triassic source rocks are dominated by vitrinite and inertinite, with V+I > 50% and alginite + amorphinite < 40%; exinite averages 2-5%. This organic matter type is Type III, and the sediments are immature to just mature. We have calculated the original organic matter richness of Ordovician deposits at selected locations. the original OM content appears to have been particularly high around Lunnan (in the North Tarim Uplift), in the Central Tarim Uplift and around Tadong (in the SE Uplift). These areas are therefore suggested to have particularly high exploration potential.