Crank oven to 350ºF.
Wash the peanuts under cool water. Drain, pat dry, and put them in a large bowl. Toss with the peanut oil and salt to coat.
Divide the peanuts between 2 half-sheet pans, making sure to spread them out in a single layer. Roast for 30 to 35 minutes, rotating the pans halfway through cooking. Remove and cool slightly prior to devouring, as they will continue to "cook," becoming crunchy as they cool.
If using peanuts to make peanut butter, remove shells and discard. Remove the skin by rubbing the peanuts together in your hands held over a salad spinner, allowing the peanuts and skins to fall into the bowl. Once the skin has been loosened from all of the peanuts, close the salad spinner, and spin until all of the skin has been separated from the peanuts.