You want to use a 3cc syringe. Use a 20g to draw the oil into the barrel. Then switch to a 23-25g pin to inject. For someone that isn't over weight, you can usually hit glutes with a 1in pin. If you have some extra fat, go with a 1.5 in. In general, a 1.5in is the safer bet for glutes. You want to bury that shot and get it deep in the muscle. For delts and quads, you can use a 1in. 

Here is a helpful article :

http://juicedmuscle.com/showthread.php?49-A-Guide-to-Safe-Injection-Technique

UC-Next Level Nutrition