> Fuel Supplier       Average MPG    # Fillups
> Arco                16.90468099    2
> Chevron             15.96717905    25
> Conoco              19.40734773    2
> Ernie's Truck Stop  12.94708029    1
> Pilot Truck Stop    18.32807571    1
> Shell               15.52268857    13
> Union 76            17.63727884    7
> Unknown             15.7309149     2

My understanding of fuel brands mirrors several others mentioned here. Not
only is the gas basically the same other than additives (which also may be
largely similar between many brands, and have little actual impact on
performance or fuel economy), but also the brand on the pump may not even be
the brand coming out of the nozzle.  Even as early as 15-20 years ago,
franchised service station owners were permitted to buy gasoline from
suppliers other than the one whose name they franchised. Gulf, for example,
only stipulated that franchisees that accepted the Gulf credit card buy
their gasoline from Gulf. If a Gulf dealer settled for accepting major
credit cards only, they could buy their gas from the cheapest bidder and
still use the Gulf name.  One difference, however, may be the consistency of
mid-grade gas. In many cases the mid-grade is literally a mixture of regular
and premium.  A recent expose here in PA claimed that in many cases the
ratio of premium was insufficient to reach the claimed octane.

I suspect that the much of the MPG difference that you are attributing to
brand may be better explained by sample-to-sample variation in driving
conditions - headwind, tailwind, hills, average speed, number of stops, etc.
If taken over a long period of time, factors such as tire pressure, tune up
and overall engine running condition, average ambient temperature, and
summer vs. winter blends also come into play. Any combination of those
differences, to my understanding, is far more likely to impact the average
MPG of a tank of gas than the brand name. Unless every thankful was used on
the identical route with no traffic and no wind over a short period of time,
the comparison is far from apples-to-apples.

- Ron Salmon
  The Bus Depot, Inc.
  www.busdepot.com
  (215)  234-VWVW

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