This report updates two earlier FTC studies on mergers and structural change in the U.S. petroleum industry. Reviewing industry developments since the 1980s, this report finds, among other things, that concentration in crude oil at the country or company level has remained relatively low and that mergers among private oil companies have not significantly affected crude oil concentration.. There have been some increases in industry concentration at other vertical levels in the domestic industry such as refining and gasoline marketing, but industry concentration for most levels of the industry has remained low to moderate. Economies of scale have become increasingly important in shaping the industry, although the incentives for firms to be vertically integrated throughout all or most levels of production and distribution have diminished. The report also describes in detail the FTC’s antitrust merger enforcement policy in the petroleum industry since the1980s.