Since I once burned out a blender motor making nut butter, I hesitate to let the machine (now a food processor) run too long. Some variables are the oil content of the nut, the age (dryness), and the size of the grinding surface. Lately I feel forced to add a little oil so that the meal switches over to butter more quickly. Ideally, no oil!

The above is the correct info. I've never even thought about adding oil to the peanuts. Or almonds. Or hazelnuts.

HLA is correct - just run the processor, or if you have one, a vitamix.

Merrill did a video awhile back making almond meal, then butter in the food processor.
I'm guessing it would work with peanuts as well, but haven't tried it.
She pulses them at first, and once they're broken up well she just runs the processor until it becomes a butter (took about 5 minutes from start to finish for her.) She does add a pinch of salt.
http://www.food52.com/blog/2228_how_to_make_almond_meal_and_butter