The oil and gas industry is usually divided into three major sectors: upstream (also called exploration and production or E&P), midstream and downstream.
[1][2] The upstream sector includes searching for potential underground or underwater crude oil and natural gas fields, drilling exploratory wells, and subsequently operating the wells that recover and bring the crude oil or raw natural gas to the surface.
[3] The upstream industry has traditionally experienced the highest number of Mergers, Acquisitions (M&A) and Divestitures.
The aggregate value of Upstream E&P assets available for sale (Deals in Play) reached a record-high of $135 billion in Q3 2013.
Examples include Patterson UTI, Trans-ocean, Nabors, Independence Contract Drilling and Cactus.