Top oil and gas companies worldwide
Companies based in the United Kingdom such as Royal Dutch Shell and BP were also among the top ten global oil and gas companies. Exxon Mobil had 13.2 billion barrels of proved oil and natural gas liquid reserves as of 2013. However, based on daily oil production, other companies such as Saudi Aramco and NIOC were among the top oil companies as of 2014. During this time, Saudi Aramco produced 8.2 million barrels per day and NIOC produced 3.8 million barrels per day. Some governments such as that of the United States provide subsidies for petroleum companies that allows for tax breaks for processes such as oil exploration and extraction.
Schlumberger, an oilfield service company based in Texas, is one of the largest equipment providers in the United States, with a total market value of nearly 107 billion U.S. dollars as of 2015. Oilfield service companies are generally not involved in oil production but instead provide equipment and services for companies undergoing exploration and production.