Oil, otherwise known as ‘petroleum or crude oil’, is a thick black liquid composed primarily of hydrogen and carbon. Oil also contains trace elements of sulphur, nitrogen, and oxygen.
Today’s oil deposits were formed millions of years ago when dead marine organisms sunk to the bottom of the ocean and were buried under deposits of sedimentary rock. Subject to intense heat and pressure, these organisms underwent a transformation in which they were converted to oil over millions of years.
This process is similar to the process of natural gas formation, however oil forms under a limited range of temperatures while natural gas forms under a wider range. This limited range of temperatures is called the ‘oil window’.

Oil is found in specific underground rocks called reservoirs. The rocks have tiny spaces in them that allow them to hold water, natural gas and/or oil. Impermeable rocks called cap rocks surround the reservoir and trap oil in its place.
Oil is extracted from the reservoir by drilling a well and pumping it up the well. Once recovered, oil is transported by pipeline, ship, rail, or truck to a refinery where it undergoes a complex process that produces petroleum products such as gasoline, diesel, jet-fuel, home-heating fuel, lubricating oil, and asphalt along with petrochemicals that are used to make common products such as plastic, drugs, synthetic fiber, soap, and paint. Approximately 71 percent of global oil consumption is used to produce fuel to power transportation systems.

Oil is a relatively abundant but is a non-renewable resource. Supplies of conventional oil have been decreasing steadily, making unconventional production more common.

Oil's benefits include its high energy density and versatility. Oil is used to produce products like transport fuels and many other common products. While all these products are important to global society, approximately 71% of global oil consumption is used to enable transportation systems.

The production and use of oil also come with many social and environmental challenges. Producing oil causes land-disturbance sometimes in environmentally sensitive areas, although this varies greatly depending on the production techniques used. The world's oil-powered transportation systems contribute significantly to global greenhouse gas emissions and climate change. Additionally, control and trade of oil resources present many geopolitical tensions between nations and, on a more local level, between stakeholder groups and communities.