In 1911, Standard Oil was broken up into 34 companies, some of which were named “Standard Oil” and had the rights to that brand in certain states (the other companies had no territorial rights). Standard Oil of New Jersey (“Jersey Standard”) had the rights in that state, plus in Maryland, West Virginia,Virginia, North Carolina, South Carolina, and the District of Columbia. By 1941, it had also acquired the rights in Pennsylvania, Delaware, Arkansas,Tennessee, and Louisiana. In those states, it marketed its products under the brand “Esso”, the phonetic pronunciation of the letters “S” and “O”. It also used the Esso brand in New York and the six New England states, where the Standard Oil Company of New York (Socony – Vacuum, later Socony – Mobil) had the rights, but did not object to the New Jersey company’s use of the trademark (the two companies did not merge until November 1999). However, in the other states, the other Standard Oil companies objected and forced Jersey Standard to use other brand names. In most states the company used the trademark Enco (“Energy Company”), and in a few “Humble”. The other Standard companies likewise were “Standard” or some variant on that in their home states, and another brand name in other states. Esso ranked 31st among United States corporations in the value of World War II production contracts.

Info gleaned from Wikipedia