Esso /ˈɛsoʊ/ is an international trade name for ExxonMobil and its related companies. The name is a phonetic version of the initials of the pre-1911 Standard Oil (SO = Esso), and as such became the focus of much litigation and regulatory restriction in the United States. In 1972 it was largely replaced in the U.S. by the Exxon brand after it bought Humble Oil, while Esso remained widely used elsewhere.