Cheap Gasoline--is it really cheap...or?

Over the last year I have been driving between Oregon and California once a month to help my mom who is 89 and broke her leg by falling. Since it’s a 600 mile drive I get to test the highway mileage on my 2002 Subaru. Strangely, I have noticed that when I buy cheap gas I get 24 to 25 miles per gallon, but when I buy Chevron or Union 76 I get 27 to an amazing 29.5 mpg. Am I nuts, or is there something about the gas? The car has 145,000 miles and was only rated for 27 on the highway when it was new so I’m happy even with the 25, but over a 600 mile trip, getting 27 to 29 pretty much negates the price difference between cheap and expensive. Is there something about cheap gas that would cause it to result in lower mileage?

Your more expensive gasoline may have a lower ethanol content than your cheaper gasoline. Ethanol does not produce as much energy as gasoline, so more of it is needed for the engine to work properly. Gasoline with no ethanol content will get you better gas mileage than gasoline with 10% ethanol added, and E85 in a flex fuel vehicle will get the worst gas mileage. This is one possible, and likely, explanation to this phenomenon you have observed, as your observed gain is typical of switching to 0% ethanol fuel.

Thanks for the comment–I wondered about that, and you may be right, but in Oregon the amount of ethanol is dictated by the State DOT, so I’m not sure this applies since all of the gas says it contains 10% ethanol by volume. I’m mystified, but the numbers do not lie–the cheap gas definitely has worse mileage. Very strange.

I agree with “Mark”. Cheap gas means little except the price per gallon. If the price structure is different from one state or county to another but the octane rating and ethanol content are the same, there should be no difference in the performance. It may also be difficult to compare if the driving environment is different? Factors including traffic conditions, hills and idling times make significant differences. You need more information to tell whether the less expensive gas actually gives fewer miles per gallon. The numbers could easily lie if you don’t consider all the factors.

Two things: you only mention the brand names of the gas that gives you good mileage.

Doesn’t California have multiple types of gas mandated by state law? Where are you buying the cheap gas, and where are the buying the expensive gas?

I have experienced this myself, before the era of ethanol and more recently.
Independent gas stations get gas from different sources from week to week.
I am convinced some batches of gas, from who knows where, have a lower energy content than others in spite of having the required octane rating.
Gasoline is a blend of several hydrocarbons, which do not burn equally hot.
Some of the ‘regulars’ on this forum have disagreed with me to the point of rudeness.

I found Valero brand gasoline to deliver consistently poor mileage.

Gasoline refiners produce regional and seasonal blends of gasoline. A gallon of Chevron bought in Miami in August will not be the same gallon of Chevron bought in Wisconsin in February.

From the API

in part

“Gasoline with a higher heating value (energy content) provides better fuel economy. Traditionally, premium gasoline has had a slightly higher heating value than regular, and, thus, provides slightly better fuel economy, but it is difficult to detect in normal driving. There can be even larger differences in heating value between batches of gasoline from the same refinery, between summer and winter volatility classes, or between brands of gasoline from different refineries because of compositional differences. The differences are small and there is no practical way for the consumer to identify gasoline with a higher-than-average heating value.”

I have found certain brands of gas give me poor performance and gas mileage…pretty consistently over the years no matter what vehicle I’ve owned. But I haven’t seen that much of a decrease in gas mileage when using those brands.

Mobil is one…For some reason I get worse performance and gas mileage…Gulf, Sunoco and Hess I get good performance from. We don’t have any of the top-tier gas companies anywhere near my house so I can’t comment on what type of performance or gas mileage I’d get using them.

Since I maybe wrongfully decided that all gasoline comes through the same pipelines, I can’t remember the last time I paid any attention to brand; just price, octane and ethanol content. Top tier, bottom tier; I couldn’t tell you which is which and neither could my cars as far as I can tell. Keeping my tires pumped up, car in tune and driving sanely seems to have much more affect on my mileage than the brand of gas.

I have never been able to detect ANY difference in mileage or performance no matter what brand or price level or octane level I choose. Wind direction and speed and whether you are gaining or losing altitude is what has much more effect on mileage than gasoline price-points…