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I usually run COSTCO or Chevron, but as an experiment I went and paid $4.099/ gal for a tank of the nitrogen formula gas at Shell.

My next previous fill-up had been at Chevron for $3.949/gal, and last night I took on 14.149gal with 332.6mi on the trip meter.

So, now I can compare actual costs, and whether it’s really better to pay less per gallon. Look at the actual numbers, so far.

Running Shell’s formulation:
The 14.149 gallons burned was composed of...
13.417gal @ $4.099/gal = $55.00 [Shell gas]
0.732 @ $3.949/gal = $2.89 [Chevron gas]

Cost: $57.89
Fuel: 14.149gal
Miles: 332.6mi
mi/$: 5.75
mpg: 23.51

Versus if I had kept running Chevron all along, at then-current $3.999/gallon:
13.417gal @ $3.999/gal = $53.65 [prior Chevron gas]
0.732 @ $3.949/gal = $2.89 [next prior Chevron gas]

Cost: $56.54
Fuel: 14.149gal
Miles: 310.7mi
mi/$: 5.50
mpg: 21.96

Versus the previous performance using Chevron’s formulation:
13.417gal @ $3.949gal = $52.98
(all fuel used was from the next previous fill-up)

Cost: $52.98
Fuel: 13.417gal
Miles: 294.7mi
mi/$: 5.56
mpg: 21.96

Comparing the performance using the Shell fuel with my prior performance running Chevron gas, I see a 7.1% increase in mpg, and a 3.4% increase in actual miles per dollar using the Shell gas.

As a control, comparing the performance using the Shell fuel with my projected performance if I had, instead, filled up at Chevron, again, basis no change in fuel economy, I see just a 1.1% reduction in actual miles per dollar, which jives with the nickle per gallon price increase between those two fill-ups.

The experiment will continue at least through the current tank of fuel to see whether the difference continues to be apparent, but so far, I’m feeling justified buying the more expensive fuel.