[Power Hungry]

All fuel calculations of that type are handled on a cost per mile type calculation.

The following examples are actual receipts from our recent trip to Orlando. The fill-up stations were the exact same stations for both fills, only one going down and one coming back. The 2.8 mile distance discrepancy is because we stopped for a bite on the trip back but for all intents and purposes it was the same trip distance. The program we ran in the truck didn't change and it was an 87 Octane based program.

87 Octane - 2.299 per Gal.
Gallons Consumed - 17.133 Gallons
Total Fuel Cost - $39.39 (yeah, I'm kooky about my fuel totals!)
Distance Traveled - 316.3 miles
Average Fuel Economy - 18.461
Cost per Mile - 12.453 cents

91 Octane - $2.469 per Gal.
Gallons Consumed - 16.606 Gallons
Total Fuel Cost - $41.00
Distance Traveled - 319.1
Average Fuel Economy - 19.216
Cost per Mile - 12.849 cents

As you can see, there was a modest economy benefit by running 91 octane on the return trip. However, even though I used less fuel, the additional cost of the fuel actually raised the cost per mile so it didn't make it cost effective. I'm sure if I'd have put an 89 or 91 octane program in the truck, we'd have seen a more significant change in economy and it may have proven worthwhile to run the 91 Octane. That test is for another day, though.

And before someone jumps in, yes I didn't take into account ambient temps, humidity, traffic, headwind, or any other environmental factor that may have had some affect on the economy outcome. But then again, life isn't a constant, controlled environment so I don't that makes the test values any less valid.

I hope this helps.