Esso (Eastern States Stanard Oil) is an international trade name for ExxonMobil and its related companies. Pronounced /ˈɛsoʊ/ ("S-O"), it is derived from the initials of the pre-1911 Standard Oil, and as such became the focus of much litigation and regulatory restriction in the United States; although other sources suggest that "Esso" is a spelt version of the pronunciation of the initials for Standard Oil. In 1973, it was largely replaced in the U.S. by the Exxon brand, while Esso remained widely used elsewhere. In most of the world, the Esso brand and the Mobil brand are the primary brand names of ExxonMobil, with the Exxon brand name still in use only in parts of the United States.