Regional studies of the petroleum geochemistry of the central and northern North Sea have been based on analyses of field sections and samples from approximately 150 released well sections available to Robertson Research International Limited. They show that hydrocarbon source rocks may occur at many levels from Cambrian to Recent, but that the principal source rock is the Kimmeridge Clay Formation and equivalent formations of Late Jurassic to Early Cretaceous age. Methods of evaluating the quality and quantity of this source rock are described and have been integrated with maturity data to obtain estimates of oil productivity. Potentially oil-generating organic matter preserved in the Kimmeridge Clay Formation is derived from both waxy plant detritus and algal material o iginating in the marine environment. The two important oil provinces of the East Shetland Basin and the Ekofish Complex contain examples of oil derived from "waxy" land plant and marine algal type source rocks, respectively. We also discuss the presence of gas in this important oil province and the distribution of low gravity oil.