Fourteen "mega" petroleum systems with Upper Jurassic source rocks contain one-fourth of the world's discovered petroleum. These petroleum systems, their locations in space and time, and their petroleum plumbing ingredients are reviewed, described, and tabulated. Each system's recovery efficiency is estimated. Plumbing ingredients are related to the relative magnitude of the petroleum system's estimated recovery efficency. While the presence of a source rock is a requirement of all petroleum systems--with source rock abundance and character of considerable influence on recovery efficiency--other plumbing ingredients are capable of even more influence on the magnitude of the systme's recovery efficiency. These other plumbing factors include the quality and quantity (extent of reservoir and cap rock, trap evolution and size, and the dynamics and timing of these factors along with source rock maturation and migration. The character, quality, and quantity of these petroleum systems' plumbing are related to their plate tectonic location, palelatitudinal realms, and the structural (tectonostratigraphic) evolution of the basin or province.