First, let me say I am not familiar with what shower or face oils are, so this may or may not apply. The imagery in my mind is an oil mixture applied directly to the skin. When working with oils, there are several things to keep in mind:
1) rate of absorption - often you want some slow absorbing and some faster absorbing, but all depends on your goals
2) comedogenic factor if applying to the face
3) medicinal benefits, even if you can't claim them