1. The Upstream Sector
The upstream oil sector is also commonly known as the exploration and production (E&P) sector.
The upstream sector includes the searching for potential underground or underwater crude oil and natural gas fields, drilling of exploratory wells, and subsequently drilling and operating the wells that recover and bring the crude oil and/or raw natural gas to the surface.
With the development of methods for extracting methane from coal seams, there has been a significant shift toward including unconventional gas as a part of the upstream sector, and corresponding developments in liquified natural gas (LNG) processing and transport.
2. The Midstream Sector
The midstream sector involves the transportation (by pipeline, rail, barge, or truck), storage, and wholesale marketing of crude or refined petroleum products. Pipelines and other transport systems can be used to move crude oil from production sites to refineries and deliver the various refined products to downstream distributors. Natural gas pipeline networks aggregate gas from natural gas purification plants and deliver it to downstream customers, such as local utilities.
The midstream operations are often taken to include some elements of the upstream and downstream sectors. For example, the midstream sector may include natural gas processing plants which purify the raw natural gas as well as removing and producing elemental sulfur and natural gas liquids (NGL) as finished end-products.
3. The Downstream Sector
The downstream sector commonly refers to the refining of petroleum crude oil and the processing and purifying of raw natural gas, as well as the marketing and distribution of products derived from crude oil and natural gas. The downstream sector touches consumers through products such as gasoline or petrol, kerosene, jet fuel, diesel oil, heating oil, fuel oils, lubricants, waxes, asphalt, natural gas, and liquified petroleum gas (LPG) as well as hundreds of petrochemicals.
Midstream operations are often included in the downstream category and considered to be a part of the downstream sector.