Top-Tier Gasoline

If you actually pay attention to commercials for cars and car-related stuff like I do, I’m sure you’ve probably heard gasoline companies proudly declare, “We’re a Top Tier Gasoline”. But what does that really mean? The terminology is so vague it makes it a challenge to figure out just what it actually is.

TOP TIER isn’t actually a rating of preference like 5 Stars on Yelp or Michelin Stars for Restaurants, like one brand being listed as being preferred over another brand – TOP TIER is actually a standard of measurement. Much like your engine’s motor oil conforms to API (American Petroleum Institute) standards, TOP TIER is a standard for gasoline, a designation given to gasoline brands that meet a minimum standard for engine cleanliness and performance, and notably  do not contain any sort of metallic additive. There is a maximum percentage of additive allowable as well as a minimum. Actually reading into this is like attempting to read a copyright contract, it’s quite complex.


This graph from 76 Gasoline illustrates the level of detergency mandated by the EPA vs TOP TIER vs 76 fuel.

This graph from 76 Gasoline illustrates the level of detergency mandated by the EPA vs TOP TIER vs 76 fuel.

Basically, TOP TIER is a designation for Gasoline that conforms to a higher standard of Purity and Performance than typical EPA standards. It does happen that some gasoline retailers provide fuels with low quality additive packages that often cause harmful buildup on injectors and intake valves and others can gunk up the combustion chamber and can hamper vehicle response.



Many Auto Manufacturers including General Motors (Cadillac, Pontiac, Chevrolet), BMW, Volkswagen and Audi all recommend their vehicles be fueled with Top Tier Gasoline. Effectively, Top Tier’s own description reads, “(The) TOP TIER Detergent Gasoline (designation) help drivers avoid lower quality gasoline, which can leave deposits on critical engine parts, which reduce engine performance.

Recently, CostCo, a favorite fuel source for many budget conscious enthusiasts, started offering Kirkland Signature TOP TIER Gasoline in its pumps – this is big, because for years, word of mouth among enthusiasts was that the fuel quality available at CostCo varied from “acceptable” to outright “bad for your car”, depending on what store you went to – because not every store had the same fuel. Anecdotal evidence litters forums with stories about gunked up valves and injectors. I’ve experienced the effects of the older “bad” CostCo gas firsthand myself – after filling my old ’90 Thunderbird Super Coupe at a CostCo with 91 Octane, the car ran terribly until I put better quality 91 Octane Fuel from a TOP TIER gasoline retailer – which happened to be SHELL – in the car. Early Forced Induction vehicles are especially sensitive to these things. Thanks to the availability of Top Tier rated fuel at CostCo, it means you can now fuel up your performance vehicle at CostCo with confidence and save a few bucks on gas, especially with gas prices inching towards $4.50/gallon again every day. 


The addition of TOP TIER means that quality fuel that is safe for your vehicle as recommended by the manufacturer is now available at the favorite fuel retailer of many, many people.

So, for those interested, let’s talk about what is in a top tier fuel. It’s worth noting that the detergency of the gas is the same regardless of what octane rated fuel you purchase.

From Base Fuel.   The base fuel shall conform to ASTM D 4814 and shall contain commercial fuel grade ethanol conforming to ASTM D 4806. All gasoline blend stocks used to formulate the base fuel shall be representative of normal U.S. refinery operations and shall be derived from conversion units downstream of distillation. Butanes and pentanes are allowed for vapor pressure adjustment. The use of chemical streams is prohibited. The base fuel shall have the following specific properties after the addition of ethanol:

  1. Contain enough denatured ethanol such that the actual ethanol content is no less than 8.0 and no more than 10.0 volume percent.
  2. Contain no less than 8 volume percent olefins. At least 75% of the olefins shall be derived from FCC gasoline as defined by CARB (advisory letter, April 19, 2001).
  3. Contain no less than 28 volume percent aromatics as measured by ASTM D 1319 or D 5580.
  4. Contain no less than 24 mg/kg sulfur as measured by ASTM D 2622 or D 5453. At least 60% of the sulfur shall be derived from FCC blend stock.
  5. Produce a 90% evaporation distillation temperature no less than 290F. as measured by ASTM D 86.
  6. Produce IVD no less than 500 mg averaged over all intake valves.

Performance Testing Chart from

Ford 2.3L Intake Valve Deposits
Base fuel
Base fuel + additive (X) at XX PTB
Ford 2.3L Combustion Chamber Deposits
500 mg min
50 mg max
Base fuel
Base fuel + additive (X) at XX PTB
Fuel Injector Fouling
<140% of base fuel
Base fuel
Base fuel + additive (X) at XX PTB
GM Intake Valve Sticking
5 or more
0 or 1
Base fuel + additive (X) at XX PTB
0 max @ 2x TOP TIER treat rate

So, how do you know if your retailer is for sure a Top Tier gasoline retailer? Well, you can check the list of retailers on or you can check your local CostCo. We hope that this has article has helped you better understand what the Top Tier Gasoline rating means for quality. For more information check out the video below, or consult the Modification Experts at ModBargains by calling us at 714-582-3330 or chat on

Story by Nicholas Gregson in Collaboration With Senior Modification Expert Alan Wei