Buick Regal 2011 Owner's Manual page 264

10-12 Vehicle Care
This vehicle was filled at the factory
with dexos approved engine oil.
Notice: Use only engine oil that is
approved to the dexos
specification or an equivalent
engine oil of the appropriate
viscosity grade. Engine oils
approved to the dexos
specification will show the
dexos symbol on the container.
Failure to use the recommended
engine oil or equivalent can result
in engine damage not covered by
the vehicle warranty. If you are
unsure whether the oil is
approved to the dexos
specification, ask your service
provider.
Use of Substitute Engine Oils if
dexos is unavailable for top up
only: Engine oil not meeting the
dexos specification or equivalent
should not be used for an oil
change. In the event that dexos
approved engine oil is not available
for maintaining proper oil level,
however, you may use substitute
engine oil displaying the API
Starburst symbol and of SAE 5W-30
viscosity grade. Extensive use of
oils that do not meet the dexos
specification, however, may result in
reduced performance or engine
damage under certain
circumstances.
Maintaining the proper oil level is
very important. However, if you use
a substitute oil for any reason, we
recommend that you perform a
complete oil change back to
dexos as soon as possible to
protect the engine and maintain the
engine's peak performance.
Viscosity Grade
SAE 5W-30 is the best viscosity
grade for the vehicle. Do not use
other viscosity oils such as
SAE 10W 30, 10W 40, or 20W-50.