The Oil industry brings to market what is currently considered the lifeblood of nearly all other industry, if not industrialized civilization itself. Oil accounts for 40 percent of the United States' energy supply and a comparable percentage of the world’s energy supply. The US currently consumes 7.5 billion barrels of oil per year, while the world consumes 30 billion per year. The U.S., and most of the world, are net importers of the resource.
The Industry can be divided into two broad themes: Upstream producers and Downstream transporters (tanker, Pipeline transport), refiners, retailers, and consumers.
Oil companies are generally categorized as "majors and "independents".
Most work in the oil field or on an oil well (upstream) is contracted out to drilling contractors and oil field service companies and the service personnel work under the watchful gaze of the client oil company, which may be a "major" or an "independent".
Petroleum is one of the non renewable natural resources and the industry is faced with the spectre of the possible eventual future depletion and exhaustion of the worlds oil supply. It is widely believed that oil exploration alone will not stave off future shortages of the resource if global future energy development fails to take this into account. The Hubbert peak theory, also known as peak oil, is an influential theory concerning the long-term rate of conventional oil production and depletion.