GMC 1995 Safari Owner's Manual page 209

In the United States and Canada, it's easy to be sure you get the right kind
of gasoline (unleaded). You'll see UNLEADED right
on
the pump. And
only unleaded nozzles will fit into your vehicle's filler neck.
Be sure the posted octane is at least 91 for premium, 89 for middle grade
and 87 for regular. If the octane is less than 87, you may get a heavy
knocking noise when you drive. If it's bad enough, it can damage your
engine.
If you're using fuel rated at 91 octane or higher and you still hear heavy
knocking, your engine needs service. But don't worry if you hear a little
pinging noise when you're accelerating or driving up a hill. That's normal,
and you don't have to buy a higher octane fuel to get rid of it. It's the heavy,
constant knock that means you have a problem.
What about gasoline with blending materials that contain oxygen
(oxygenates), such as MTBE or alcohol?
MTBE is "methyl tertiary-butyl ether." Fuel that is no more than 15%
MTBE is fine for your vehicle.
Ethanol is ethyl or grain alcohol. Properly-blended fuel that is no more than
10% ethanol is fine for your vehicle.
Methanol is methyl or wood alcohol.
NOTICE:
Fuel that is more than 5% methanol is bad for your vehicle.
Don't use it. It can corrode metal parts in your fuel system and
also damage plastic and rubber parts. That damage wouldn't be
covered under your warranty. And even at 5% or less, there
must be "cosolvents" and corrosion preventers in this fuel to
help avoid these problems.
Gasolines for Cleaner Air
Your use of gasoline with deposit control additives will help prevent
deposits from forming in your engine and fuel system. That helps keep your
engine in tune and your emission control system working properly. It's good
for your vehicle, and you'll be doing your part for cleaner air.
Many gasolines are now blended with oxygenates. General Motors
recommends that you use gasolines with these blending materials, such as
MTBE and ethanol. By doing so, you can help clean the air, especially in
those parts of the country that have high carbon monoxide levels.
In addition, some gasoline suppliers are now producing reformulated
gasolines. These gasolines are specially designed to reduce vehicle
emissions. General Motors recommends that you use reformulated gasoline.
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