However, generally speaking, a 2003 Ford Taurus likely uses:
* 5W-20 This is a common viscosity for newer vehicles, and it's quite possible your Taurus uses this.
* 5W-30 This is another common viscosity, and may be an acceptable alternative depending on the climate and your engine's specific requirements (again, check your manual).
Crucially: The owner's manual will also specify the type of oil (conventional, synthetic blend, or full synthetic). Using the wrong type of oil can damage your engine. Don't rely on online guesses; consult your owner's manual.