> All of this should be considered along with the driving environment.
It
> seems that an engine under higher and prolonged loads, such as a
> hill-climbing Westy, is probably going to benefit from the more
expensive
> gasoline.

in my experience, the octane makes no difference in MY buses ... not a
nickel's worth of difference. over the years, i've tried to even up
the tankfuls of the three octanes available in my area, just for
testing purposes. but since i'm cheap, the 87 octane usually has twice
as many tankfuls as the other two octanes. ;)

here's the results ...

1988 Vanagon
Thursday   27 Dec 2001                                         Page  1

Brand   Oct Tanks    Gals     Cost     Miles    MPG $/g   $/mi
Amoco   R87    46   592.0   654.38  12,077.3 20.4 1.11  0.05
Bp          R87    46   574.5   627.48  11,577.0 20.2 1.09  0.05
Chevron  R87    46   617.6   689.15  12,214.0 19.8 1.12  0.06
Exxon     R87    46   617.5   679.13  12,270.3 19.9 1.10  0.06
Shell       R87    46   595.6   665.00  11,553.2 19.4 1.12  0.06
Unocal    R87    43   580.1   618.57  11,418.2 19.7 1.07  0.05
Z-other    R87     2    27.0    28.62        533.6 19.8 1.06  0.05
Z-start     R87     1    15.7    14.10            0.0  0.0  0.90 14.10
      Total        276 3,620.0 3,976.43  71,643.6 19.8 1.10  0.06

Amoco   R89    23   300.2   343.26    5,774.0  19.2 1.14  0.06
Bp          R89    23   313.6   367.39    6,231.3  19.9 1.17  0.06
Chevron  R89    24   309.1   375.84    6,283.3  20.3 1.22  0.06
Exxon     R89    23   297.8   345.06    5,655.4  19.0 1.16  0.06
Shell       R89    23   301.6   353.11    5,997.0  19.9 1.17  0.06
Unocal    R89    21   269.1   311.73    5,332.1  19.8 1.16  0.06
      Total         137 1,791.4 2,096.39  35,273.1 19.7 1.17  0.06

Amoco   P92    25   333.5   440.92   6,605.9 19.8 1.32  0.07
Bp          P92    25   308.9   397.89   6,139.3 19.9 1.29  0.06
Chevron  P92    25   316.2   418.87   6,377.1 20.2 1.32  0.07
Citgo       P92     1       9.7     15.52     101.7 10.5 1.60  0.15
Exxon     P92    25   315.5   410.99   6,427.0 20.4 1.30  0.06
Shell       P92    25   325.5   413.68   6,561.0 20.2 1.27  0.06
Unocal    P92    21   274.1   349.98   5,581.4 20.4 1.28  0.06
Z-other   P92     1        3.5      4.28        55.6 15.9 1.22  0.08
      Total       148 1,886.9 2,452.13  37,849.0 20.1 1.30  0.06

Totals            561 7,298.3 8,524.95 144,765.7
Averages per Tank       13.0   15.20     258.0 19.8 1.17  0.06

the z-start is the very first tank i put into the bus. i separated it
out like that to keep from lowering the stats for the brand/octane.
z-other is off-brands that i used over the years ... when i couldn't
find a station that i had a credit card for. :)

to my untrained statistical eye, there ain't a bit of difference
between them. now, it LOOKS like the premium is slightly higher. and
if you didn't know me, you'd think that, too ... but my tendency is to
fill up with premium only before  a trip, so the mpg is a bit skewed
that way: the 91/92/93 (all condensed into 92 octane) gets a tad more
highway miles than, say, the 87 octane (which gets used mostly on
around-town trips).
and i don't think that 0.5 mpg would be a 'significant' result, in
this more-or-less unscientific test of mine. too many variables, i
think. :)

anyway, as far as i'm concerned, in MY buses, using the gasolines
available in MY area of the country, and with MY driving style, there
ain't enough difference to warrant use of the more expensive
gasolines.

so why do i do it? :) old habits die hard ... i kinda semi sorta
somewhat think or believe that maybe, just maybe, the higher octane
fuels 'clean' the injectors or something. oh, and i'm trying to be
fair in the test. yeah, that's it! ;)

unca joel
1988 GL
1987 GL Camper
1991 Carat