Unit of energy
The tonne of oil equivalent (toe) is a unit of energy defined as the amount of energy released by burning one tonne of crude oil. It is approximately 42 gigajoules or 11.630 megawatt-hours, although as different crude oils have different calorific values, the exact value is defined by convention; several slightly different definitions exist. The "toe" is sometimes used for large amounts of energy.
Multiples of the "toe" are used, in particular the megatoe (Mtoe, one million toe) and the gigatoe (Gtoe, one billion toe). A smaller unit of kilogram of oil equivalent (kgoe or koe) is also sometimes used denoting 1/1000 toe.
Definitions.
The International Energy Agency defines one " tonne of oil equivalent" (toe) to be equal to:
Conversion into other units:
Some other sources and publications use divergent definitions of toe, for example:
Conversion factors.
Tonne of oil equivalent should be used carefully when converting electrical units. For instance, BP's 2022 report used a factor of 40% efficiency (the average efficiency of a standard thermal power plant in 2017), or roughly 16.8 GJ per toe, when converting kilowatt-hours to toe. BP's model is also based on the assumption that efficiency will increase linearly to 45% by 2050. 
Derived units.
For multiples of the tonne of oil equivalent, it is more usual to speak of millions of tonnes of oil equivalent and kilotonnes of oil equivalent (ktoe).
References.
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