This is FYI hearsay, something I read on this list (I think).

Mis Grade fuel is a marketing ploy to help fuel companies get rid of a
strange product. If I recall all the details correctly,  There are only
three fuels pumped by refineries and large pumping outlets to regional
distribution "tank farms": regular gas, which is then branded and additive
packages added by various oil companies; high octane, which is then branded
and additive packages added by various oil companies; and Amoco Ultimate
which is special, and the pumping pipes and tanks go through special
"cleansing flow" to make sure it is pure.

Mid grade is the swill that comes out of the pipe when they switch from
regular to high octane or vice versa, and the gas is mixed. For marketing
reasons, they can't throw it away, so they sell it a "mid grade". The
octane varies widely.

Cheers,

G. Matthew Bulley
Bulley-Hewlett & Associates
www.bulley-hewlett.com
Cary, NC USA
888.468.4880 tollfree

-----Original Message-----
From:   J. Eric Pitman [SMTP:norton85@BELLATLANTIC.NET]
Sent:   Tuesday, July 13, 1999 7:07 PM
To:     vanagon@GERRY.VANAGON.COM
Subject:        RE octane rating

 << File: ATT00001.htm >> I run Mid Grade Gas in my 84 Westfalia. Runs
horrible on reg. and lousy mileage, On high test it makes no differance
than the mid grade for the Van, No hard facts, but I have put 100,000 miles
on my Westy in the last 4.5 years and it works for me.
Eric P. 1984 Westfalia (Green Hornet)