The term BYGONE GAS can be solved by the crossword solution ESSO, which is a four-letter word. ESSO is a brand of gasoline and motor fuel that was first introduced in the United States in the early 1900s. It is now owned by ExxonMobil, one of the world's largest oil and gas companies. The name ESSO is derived from the initials of the Standard Oil Company of New Jersey, which was the original owner of the brand.