The Enco brand was introduced by Humble in the summer of 1960 at stations in Ohio, but was soon blackballed after Standard Oil of Ohio (Sohio) protested that Enco (Humble's acronym for "ENergy COmpany") sounded and looked too much like Esso as it shared the same oval logo with blue border and red letters with the two middle letters the only difference.

Despite the success of the "Put A Tiger In Your Tank" advertising campaign introduced by Humble in 1959, to promote its Enco/Esso Extra gasolines, the similar oval logotypes, the Happy Motoring!

tagline used in advertisements that also appeared overhead of service bays at each station, use of the Humble name in all Esso/Enco ads and the uniformity in design and products of Humble stations nationwide, the company still had difficulties promoting itself as a nationwide gasoline marketer competing against truly national brands such as Texaco — then a 50-state marketer and the only company selling products under one brand name in each state.

The name change, one of the most expensive in the history of the U.S. oil industry, not only involved advertisements and identifying street signs at service stations, but also gasoline pumps, product packaging, tankers, transport and delivery trucks, hundreds of smaller signs at more than 25,000 service stations, and millions of credit cards sent to account holders to replace their previous Esso/Enco cards.

In 1957, scientists from Humble Oil published a study tracking “the enormous quantity of carbon dioxide” contributed to the atmosphere since the Industrial Revolution “from the combustion of fossil fuels.” Exxon was aware of these findings and later researched the effect of its own company on global warming.

Monterey County was deeply divided on the plan with tourism proponents, some agricultural interests and a nascent environmental movement opposing the refinery.

However, public opinion surveys showed greater than 2 to 1 support for the Humble Oil refinery with Warren Church supervisorial district in favor with 82%.

[19][20] The Salinas Californian stated, “It is conceivable in the future that other areas debating the admittance of an oil refinery will look at Monterey County as an example of strict regulations.

[11] On May 18, 1966, Humble Oil announced a suspension of all activities at Moss Landing, publicly stating that a prime reason for abandoning the site was the difficulty of achieving a permit for a larger refinery.

[22] Public outcry and a legal challenge plus engineering problems also discouraged Humble Oil, and they eventually pulled out of Monterey County and decided to build a bigger refinery up north in more-welcoming Benicia.