The Petroleum Equipment Institute is a trade association whose members manufacture, distribute and service petroleum marketing and liquid-handling equipment.The Petroleum Equipment Institute is located in Tulsa, Oklahoma, and is a not-for-profit corporation.Founded in 1951, PEI represents over 1,600 member companies located in all 50 states and over 80 countries. Members include manufacturers, sellers and installers of equipment used in service stations, terminals, bulk plants, fuel oil and gasoline delivery, and similar petroleum marketing operations.