The list of oilfield service companies includes companies that provide services to the petroleum

Petroleum

Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

 exploration and production industry but that do not typically produce petroleum themselves. Given the many mergers and acquisitions that have occurred in this sector, acquired companies are listed as sub-lists of their (current) parent companies, as nearly as articles.