The EPA requires a minimum amount of detergent in gas, but many people say it is not enough. In the jargon, the Lowest Additive Concentration allowed is called the LAC. At right are some BASF photos showing how the LAC rate is not that much better than no additive.
"Top Tier" gas is trademark held by a consortium of 27 gasoline retailers, big and small -- like Chevron, Exxon-Mobile and Shell, but also including Kwik-Trip. Four automakers, Toyota, GM, Honda and BMW negotiated standards with the gas retailers, and these companies recommend Top Tier gas.
This gas will provide better cleaning action than specified by the EPA minimum standards, and keep valves from sticking. This will improve economy, reduce emissions, and presumably lengthen engine life.
All the gasolines at the "Top Tier" stations will meet the standard, and this means the economy grade will meet the standard, just like the premium. Marketing-wise, it hurts the ability to differentiate.
BP is following a different path. Specifically, their premium gas has more detergent than their regular -- if you believe the website. The former Amoco Oil company, now part of BP, advertised its detergent gasolines prior to the new EPA standards. They are not a member of "Top Tier," and they are endorsed by Ford, who also is not allied with "Top Tier." The range of quality at BP bothers me, since now I don't know which grade of gas to buy.
I'd like to talk about what these detergent additives are, but this is one of those industries, where compositions are all trade secret. Dow says they are sulfonates, phenates and salicylates.
In summary, it is probably best to trust the judgement of the auto manufacturers, since they do not have a interest in selling overpriced gasoline. If GM, Toyota and Ford all think that gas with the LAC of detergent is not good enough, then I will upgrade to a better quality of gas. Good bye Marathon.