Why can you buy gas with an 85 octane rating in Colorado when the standard is usually 87?

Jenn Henry
Why are there regional variations in octane ratings? Why do some Rocky Mountain states allow 85, 85.5, 86, or 86.5 octane fuel to be sold?

Image courtesy Upupa4me.

You guessed it. Law! And the standards law relies on. And altitude.

Higher octane ratings mean the fuel is higher performing, or that it is better able to resist combustion (especially uncontrolled burn, or “engine knocking”).

Many states, including Colorado, peg their laws on the American Society for Testing and Materials standard. ASTM is a standards development organization founded in 1898. By statute, Colorado can legally sell whatever the ASTM determines it can. Go read the statute below–it’s kind of crazy!

An American Petroleum Institute study showed that cars would perform as well using 85 at high altitude as they would using 87 at lower altitude. Refineries can’t sell 85 many places, and it is cheaper to produce–so it is cheap to buy in Colorado.

Since 1984, however, cars have been manufactured to automatically adjust for altitude as cars have shifted from carburetors to fuel-injection engines. A 2001 study from the Colorado Legislative Council (the state legislature’s research group) called into question the 85-is-fine-at-high-altitude finding for newer cars.

In 2006, ASTM acknowledged it might be time to take another look at this standard. But the standard apparently hasn’t changed. To this day, you can still buy 85 at Colorado pumps.

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