Octane Geography

Hey Matt:

When I recently drove through Utah, I noticed that "regular" grade gasoline (in addition to costing a lot less) is 85 octane, not 87 like it is here. I thought this was maybe some odd Mormon custom, perhaps to discourage wasteful consumption, until I saw the same thing in Colorado. What gives with these lower-cost, lower-octane fuels? My car runs fine on them. Why can't we get them here in California, and maybe save a few pennies at the pump?

-- Robert Sheaffer, East County

Your 85-octane trail must have gone through high-altitude locations-- Salt Lake City, Denver, right? The lower atmospheric pressure and oxygen levels at these spots require a different gas blend so your carburetor has the right mix of air and fuel for proper combustion. (Octane is a measure of combustability of the fuel.) If we used 85 octane here at sea level, or anywhere below about 5000 feet, we'd hack and cough our way down the road and eventually chug to a halt. True, 85 octane gas will be cheaper than 87, but the difference won't be huge. Any big cost differences you saw are more likely a result of the always-mysterious gas company pricing patterns you see around the country.

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