What is it?
Oil is a liquid formed from ancient plants and animals which have been turned to rock (fossilised) over millions of years.
Oil rises up through the earth and underground lakes of it form when the oil comes up against types of rock which won't let it pass.
Pipes are drilled down under the land or sea to where the oil lies sandwiched between layers of rock. The oil is pumped up to the surface and transported by tankers or pipelines.
Reliable technology, well established. The UK has its own supply from the oil fields of the North Sea.
Oil is a non-renewable fossil fuel, that means if we use it all up we can't get any more. Burning oil releases the greenhouse gas carbon dioxide.
The price of oil goes up and down a lot, that makes it hard for power companies to plan ahead. The supply can also be interrupted by war as lots of oil comes from parts of the world where there is conflict.
Making electricity using oil is not very efficient.