With gas prices holding at $4 a gallon, I’m averaging $60 a tank to fill my Maxima with cheap gas. Yet last month, I actually made a net profit on the machinations of Big Oil. Here comes the math:
Gas: -$120
Discover Gas Card Cashback: +$5
Energy Stocks ETF (XLE) Gain: +$134
Total: +$19
So this month I beat Big Oil! 
My fortunes will probably change next month, though; I usually average 3 tanks.
Sustained $4 a gallon gas is one of the new signs of the apocalypse, meaning it’s time to question the ancient Japanese wisdom of my Maxima’s owner’s manual: “Premium fuel recommended”.
My now vestigial mechanical engineering degree had been able to follow the logic: a high compression engine needs purer fuel to run at peak efficiency, otherwise the engine electronics would just dial it back to a less efficient level. Cheaper gas would just be offset by fewer miles per gallon.
As much as love watching my holdings in energy stocks go up, I decided it was time to put this to the test: would I really get fewer miles out of non-premium gas? My admittedly loose testing methodology: two tanks of typical driving measuring cumulative miles per gallon on a ScanGauge.
The results: 22 mpg on premium, 21 mpg on regular. That 1 mpg is well within my margin of error, particularly given that I did more highway driving on the premium tank. I’ll keep watching the numbers to see if there’s a longer-term decline, but for now regular fill-ups are going to ease the pain at the pump a bit. How does your mileage vary?
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