Naftogaz of Ukraine is the largest national oil and gas company of Ukraine. It is a state-owned company subordinated to the Government of Ukraine. The vertical-integrated company carries out a complete cycle of exploration operations and development of deposits, operating and exploratory drilling, extraction, transportation, and refinement of natural gas and crude oil, supply of natural and liquefied gas to consumers.

United Energy Systems of Ukraine, (UESU), was a natural gas trading company in Ukraine. In the years 1995 and 1996, it was the largest natural gas importer in Ukraine. The company was affected by a series of financial irregularities leading to criminal charges against the principals and closure of the company in 2009.