Oil shale

Oil shale is a sedimentary rock which can be squeezed to get oil out if it. The part which has oil in it is called kerogen. There's a great deal of it, and the oil is said to be "oil in place". It is planned as a source of oil after regular oil wells dry up.^[1]

So far only Estonia and China have got big oil shale industries, but other countries plan to develop it. The forests of ferns and trees which originally made the oil were very widespread on Earth, so in theory many other countries have oil-bearing land.

Alternatively, there are people who believe that hydrocarbons are not biogenic. They think hydrocarbons were formed in space and delivered to planets like Earth ready-formed. Although this might seem far-fetched, it has been suggested by some notable scientists, such as Thomas Gold.

1. ↑ "Oil shale and other unconventional fuels". United States Department of Energy. Retrieved 9 February 2014.