Source-bed reservoir relations are inferred from statistic and lithologic study of oil fields of southeastern U.S. and Permian basin. Source-bed lithologies have distinct petroleum characteristics; oil gravity and gas-condensate conversion points are related to depth of burial. Gray and green shale may produce oil of higher gravity for equal depth than black or brown shale, implying that open-marine waters produce higher gravity oil than stagnant marine waters. Analysis of world examples confirms structural updip yet stratigraphic downward migration of oil from its source if principal source is above oil pool. Overburden of about 2,000 feet is needed for flush migration from source to sizable pool; earliest accumulations are essentially gas. Isopachous maps of intervals 2,000-3,000 feet above source bed will reveal structures present during migration.