Heat your oven to 250 degrees.
If you prefer seasoning, now is a good time to season your roast. If this was done at your local market than it is ready to cook. There are many ways to season a roast and in my experience, dry rubs work as good as anything. A couple of other options include Rosemary and olive oil. You may place a few sprigs of fresh Rosemary on top of the roast to add flavor. The olive oil can be rubbed over the roast as well to add to the flavor. Please keep in mind that these will add different flavors to your meat and not everyone (including you) may like it.
Place the roast fat side up, uncovered, in a roasting pan. Place the pan in the oven and bake approximately 30-40 minutes per pound.
To be on the safe side, buy and use a meat thermometer.
Remove roast from the oven at 138 for rare, 142-145 for medium-rare, and 147 and up for well.
Larger roasts (approximately 10 lbs. and up) tend to cook faster than times listed to watch your thermometer.
After the desired temperature is achieved, pull the roast out of the oven and let it sit for about 15 minutes. In this fifteen minutes, it will actually cook an additional 5 degrees before it starts cooling off. After the fifteen minutes, it is ready to carve and serve.
4-6 lbs. 2.5-4 hours
6-8 lbs. 4-5.5 hours
8-10 lbs. 5.5-6 hours
10-12 lbs. 6.5-7 hours
12-16 lbs. 7-9 hours
Temperatures may be adjusted to speed up or slow down the cooking process.
All cooking times are approximate. Oven temperatures will often vary and depend largely on factors like conventional or convection ovens. Always use a reliable meat thermometer! I cannot stress this enough. They are inexpensive and last a long time. It is the cheapest insurance for any of the cooking that you do. These instructions are only my suggestion, and cetainly not the only method for cooking your Prime Rib.