Petroleum engineering is a branch of engineering science concerned with locating and accessing and production of Hydrocarbons which includes crude oil or natural gas sources. Exploration and production are considered to be part of the oil and gas industry's upstream segment. The oil and gas industry's two primary subsurface disciplines are exploration, which is carried out by earth scientists, and petroleum engineering, which focuses on maximizing the economic recovery of hydrocarbons from subterranean reserves.
The transformation of crude oil (petroleum) and natural gas into products or raw materials is studied under petrochemistry, a branch of chemistry. Petrochemicals have grown to represent a significant element of the chemical industry today.