Petroleum, also known as crude oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. It is a fossil fuel and nonrenewable source of energy. Petroleum was formed from the remains of ancient marine organisms such as diatoms that lived millions of years ago in a marine environment before dinosaurs existed. Over millions of years, the remains of these animals and plants were covered by layers of sand, silt, and rock. Heat and pressure from these layers turned the remains into what we now call crude oil or petroleum.
Petroleum is mainly a mixture of hydrocarbons, i.e. containing only carbon and hydrogen. The most common components are alkanes (paraffins), cycloalkanes (naphthenes), and aromatic hydrocarbons (e.g. benzene and toluene). They generally have from 5 to 40 carbon atoms per molecule, although trace amounts of shorter or longer molecules may be present in the mixture.
Petroleum is used to make gasoline, an important product in our everyday lives. It is also processed and part of thousands of different items, including tires, refrigerators, life jackets, and anesthetics. When petroleum products such as gasoline are burned for energy, they release toxic gases and high amounts of carbon dioxide, a greenhouse gas. Carbon helps regulate Earth’s atmospheric temperature, and adding to the natural balance by burning fossil fuels adversely affects our climate.
Petroleum is recovered by oil drilling and then refined and separated into different types of fuels. Petroleum contains hydrocarbons of different molecular weights and the denser the petroleum the more difficult it is to process and the less valuable it is.
