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Quad: A measure of energy equal to one trillion BTUs; an energy equivalent to approximately 172 million barrels of oil.
A quad is a unit of energy equal to 1015 (a short-scale quadrillion) BTU, or 1.055 × 1018joules (1.055 exajoules or EJ) in SI units.
The unit is used by the U.S. Department of Energy in discussing world and national energy budgets. The global primary energy production in 2004 was 446 quad, equivalent to 471 EJ. 
Some common types of an energy carrier approximately equal to 1 quad are:
- 8,007,000,000 gallons (US) of gasoline
- 293,071,000,000 kilowatt-hours (kWh)
- 293.07 terawatt-hours (TWh)
- 33.434 gigawatt-years (GWy)
- 36,000,000 tonnes of