To make the best quality roasted peanuts in-shell, make sure to spread the peanuts evenly over the baking sheet, and roast them at 350 degrees Fahrenheit for 30 to 35 minutes, turning once halfway through the roasting time. Use about 1 tablespoon of peanut oil per pound of peanuts.
If eating the roasted peanuts right out of the shell, use Virginia or Valencia peanuts. If making peanut butter, Spanish peanuts are best due to their high oil content. Make sure to thoroughly wash and coat the peanuts in oil prior to baking, and allow them to cool for a few minutes after removing them from the oven.