Most likely your fuel pump or fuel rail is leaking oil into your crank case. It can also bypass the piston rings.
Either way you have a potentially dangerous situation as the engine can and eventually will run away on you. A run away engine will usually destroy itself in a spectacular fashion. Broken crank shafts, twisted connecting rods or pistons hanging out the side of the engine block are not uncommon.
Check you compression, if that's ok have your fuel system rebuilt. If your engine has a lot of hours on it you may want to consider an entire rebuild.
Either way you have a potentially dangerous situation as the engine can and eventually will run away on you. A run away engine will usually destroy itself in a spectacular fashion. Broken crank shafts, twisted connecting rods or pistons hanging out the side of the engine block are not uncommon.
Check you compression, if that's ok have your fuel system rebuilt. If your engine has a lot of hours on it you may want to consider an entire rebuild.