If you have ever purchased all natural peanut butter in your life, the first time you go to use it, the oil has separated from the peanut butter and is sitting on the top of the jar. If you take a spoon and try to stir it up, you always wind up spilling some of the oil all over the outside of the peanut butter container.
You could empty the peanut butter jar, re-stir the oil and the peanut butter back together again, but with all the effort required to get it back in the jar you might as well have just stirred it in the jar. If you don't feel like hand mixing it, you can use another very simple technique.
When you get home from the grocery store, flip the peanut butter
When you finally go to open your peanut butter, you will notice that there isn't an inch of peanut oil sitting at the top of the container. The peanut butter will require no mixing and is ready to eat immediately. I also suggest storing your natural peanut butter upside down to prevent the bottom peanut butter from being extremely dry.