What ingredient would you double in order to make a cake super moist?

I keep seeing dry carrot cake. If you double the oil in it will it be super moist? Or what other ingredient would make it super moist?
It should be something that would cause me to break out. Yes; in pimples like a jr high kid. I figured oil could have done it when I found a really moist carrot cake that’s too expensive and that, yes, broke me out.