About 29% of electricity used by the petroleum refining industry is produced onsite, primarily by means of cogeneration. The refining industry is the third largest cogenerator in the manufacturing sector. Cogeneration can provide competitive advantages over purchased electricity, since thermal efficiencies are much higher and excess electricity can be sold back to the grid. Petroleum refineries have steadily increased cogeneration capacity, which has nearly tripled since 1985. [MECS 1994]