* Cracked or damaged piston rings: This is the most common cause. Worn or broken piston rings allow combustion gases (containing gasoline) to leak past the pistons and into the crankcase where the oil is. This will cause the oil to be diluted with gasoline, reducing its lubricating properties and potentially causing catastrophic engine damage.
* A severely damaged or failed head gasket: A blown head gasket can allow coolant or combustion gases (again, containing gasoline) to leak into the oil. This will also contaminate the oil, though often with a milky appearance from the coolant mixing with the oil.
* Fuel pressure regulator failure: A faulty fuel pressure regulator could potentially leak fuel into the intake manifold vacuum system, which in turn might find its way into the crankcase via the PCV (Positive Crankcase Ventilation) system. This is less common than piston ring or head gasket failure for a large amount of fuel in the oil.
Identifying the problem requires investigation: Checking the oil level and its appearance is the first step. Oil contaminated with gasoline will often smell strongly of gasoline and might appear thinner or have a slightly different color. A mechanic would need to perform a compression test, and potentially a leak-down test, to diagnose the issue accurately. Simply adding oil won't solve the problem and may worsen it; the underlying mechanical failure needs to be addressed.
