Toyota 2003 Prius Owner's Manual page 220

156.ENGINE OIL SELECTION
"Toyota Genuine Motor Oil" is filled in
your Toyota vehicle. Use Toyota approved
"Toyota Genuine Motor Oil" or equivalent
to satisfy the following grade and viscos-
ity.
Oil grade:
API grade SL "Energy–Conserving" or
ILSAC multigrade engine oil.
Recommended viscosity:
SAE 5W–30
oil008
Temperature range anticipated before next
oil change
SAE 5W–30 is the best choice, for good
fuel economy, and good starting in cold
weather.
If SAE 5W–30 oil is not available, SAE
10W–30 oil may be used. However, it
should be replaced with SAE 5W–30 at
the next oil change.
82P103
API service symbol
ILSAC certification mark
213