Chevrolet Repair: gas smell in my oil, fuel pressure regulator, combustion gasses

Question
 what can cause gas to get down into oil

Answer
You haven't told me what vehicle you have...fuel inj or carb, etc.

I'm assuming you have fuel injection. Possible causes of oil getting into the gas could be leaking fuel injectors or possibly depending on what model you have, a defective fuel pressure regulator. A worn engine causing too much combustion gasses getting past the rings.