Ford 1996 Contour Manual page 202

Servicing Your Contour
Typical octane rating label
Using a fuel with a lower octane rating can cause persistent and
heavy knocking, which can damage the engine.
Do not be concerned if your vehicle sometimes knocks lightly
when you drive up a hill or when you accelerate. However, see
your dealer or a qualified service technician if persistent heavy
knocking occurs because this can damage the engine.
If your vehicle has problems with starting, rough idle or
hesitation problems when the engine is cold, it may be caused
by fuel with low volatility. Try a different brand of fuel. If the
condition persists, see your dealer or a qualified service
technician.
Gasolines for clean air
Fuels in certain areas of the country are required to contain
oxygenates to improve air quality. Common oxygenates are
ethanol or grain alcohol (blended at no more than 10%),
methanol or wood alcohol (blended at no more than 5% with
cosolvents and additives), and MTBE or methyl tertiary butyl
ether (blended at no more than 15%).
Reformulated fuel is also required in certain areas of the U.S.
These fuels are designed to further reduce the emissions from
your vehicle.
205