I use about a 20 or 22 gauge to draw. That works for common oils like MCT or GSO. For a 10 mL vial I'll drop about 8 mL of air in the syringe, push three or four mL of air into the vial and then draw 4 ml of oil. Then some more air. pull oil, like that. I find you don't need 10 mL of air at one time but it's better to use a bit less air than total oil and push the air in about a quarter or a third at a time.
Also like
@Dirthand said, If you warm it up it'll be super easy, but for MCT or GSO shouldn't be necessary.