With the 3.0L V6 it can be either steel or aluminum. The 24V DOHC V6 will have an aluminum oil pan and I believe the 24V engine was only available on the LX trim line (there are usually badges to denote the 24V duratec engine). The older style 3.0 (pushrod engine) has a steel pan
You can verify by looking under your car with a flashlight. The steel pan will be smooth (it is stamped) and often is painted black. The aluminum pan will look like a casting I believe. I am referring the engine oil pan
An easy way the tell if your oil pan is steel or aluminum is to touch it with a magnet. The magnet will stick to steel but not aluminum. Please make sure you are checking the engine oil pan, not the transmission oil pan!