Peanut butter pro tip:
If you buy the stuff that needs significant stirring before first use, skim some of the oil off right after you open the jar. Save and refrigerate the oil. Stir peanut butter well. When you get to the bottom third of the jar, when the contents are getting dry and crumbly, add some of oil back in.
Or you could do what I do. Dump the entire jar in to a small mixing bowl, stir it well and put it back in the jar. If you mix it well the oil will stay mixed in unless it is stored for a long period of time. I don't have that problem though. I usually go through a jar in a few weeks.