Petroleum, a fossil fuel found in geological formations beneath the Earth's surface and was formed from the remains of ancient marine organisms and a nonrenewable energy source as it takes millions of years to form. Refining petroleum is the process of converting crude oil into various useful products, such as gasoline, kerosene, gas oil, lubricating oil, residual fuel oil, bitumen, and paraffin under increasing temperature. Petroleum is found in underground pockets called reservoirs. A typical petroleum reservoir in which oil is trapped is mostly sandstone or limestone.
Petroleum is vital to many industries and a major part of the chemical makeup of many plastics and synthetics. Oil accounts for a large proportion of the world's energy consumption. Steps involved in petroleum industry are processes of investigation, extraction, refining, transporting mainly through pipelines and oil tankers and marketing products. Classification of petroleum is mainly based on the geographic location it is produced and its API gravity. To minimize the negative impacts on the environment the production, transportation, distribution, and consumption of petroleum are strictly regulated.