Olive oil does make a good sun tanning oil that is natural and it contains Vitamin E that is an antioxidant which can help prevent damage to the skin.
For best results though when using Olive Oil for sun tanning you should use the Olive Oil that states it's Extra-Virgin'.
However be aware that the Olive Will not protect your skin from the UV rays from the sun like regular sun tanning lotion will but the Olive Oil is good for sun tanning either way.