2003 Toyota Prius Owners 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 viscosity. Oil grade: API grade SL "Energy-Conserving" or ILSAC multigrade engine oil. Recommended viscosity: SAE 5W-30 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 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. ILSAC certification mark 213