Esso is an international trade name for ExxonMobil and its related companies. The name is derived from the initials of the pre-1911 Standard Oil, Eastern States Standard Oil, 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. In most of the world, the Esso brand and the Mobilbrand are the primary brand names of ExxonMobil, with the Exxon brand name still in use only in the United States alongside Mobil.
Info gleaned from Wikipedia