Generally, the oil and gas industry is structured into three main streams, the Upstream, the Midstream, and the Downstream as depicted in Figure 9. 

The Upstream industry, also known as the Exploration and Production sector (E&P) finds and produces crude oil and natural gas using specialized technologies to search for and eventually win and cart away hydrocarbons found underground and underwater. It finds the oil and gas using seismic tools, and then drill and complete the wells using drilling and completion rigs. The wells are then tied through pipeline or flowlines to a production centre called the flowstation, for separation and treatment, before they are injected into export lines to the export terminal.

The Midstream segment processes, stores, markets and transports commodities such as crude oil, natural gas, natural gas liquids (NGLs, mainly ethane, propane and butane) and sulphur This segment provides the vital link between the far-flung petroleum producing areas and the population centres where most consumers are located. It also connects the upstream sector to the downstream sector through pipelines and other transport systems. Major activities undertaken in the midstream include; transportation (pipeline, rail, barge, oil tanker, and/or truck) and marketing of wholesale products.  

The Downstream industry includes oil refineries, petrochemical plants, petroleum products distributors, retail outlets and natural gas distribution companies, and therefore is more people oriented as it touches more people than the upstream and midstream through its vast products such as gasoline, diesel, jet fuel, heating oil, asphalt, lubricants, synthetic rubber, plastics, fertilizers, antifreeze, pesticides, pharmaceuticals, natural gas and propane, liquefied petroleum gas (LPG), asphalt, petroleum coke, gasoline, fertilizers, antifreeze, plastics, rubbers, pesticides, synthetic rubber, jet fuel and many more.   Figure 9 depicts the different streams or segments in the oil and gas industry.

Figure 9: Distribution of the Oil and Gas Sectors.

Figure 10: Different operating terrain in the Oil and Gas Industry.

Besides the categorization into the various streams or segments, there is also another classification based on the terrain or working environment, and these are categorized into Onshore or land, Swamp, Shallow waters, with water depths from 5 – 50 meters, and Offshore from 100 – 300 meters of water depth, Deep Offshore from 300 meters to 1500 meters of water depth, while Ultra deep basins are those with water depths higher than 1500 meters. (Figure 10).