Gasoline in the oil. This is a very serious condition that can cause irreparable damage to the engine. The life blood of the engine is being diluted with gas. This can be cause by a leaking injector, bad fuel pressure regulator, or on and engine with a carburetor, float level to high, needle valve & seat that are bad. Have this fixed ASAP!
Also if it is bad then your fuel pump could be over pressurizing the system, but usually the fuel pressure regulator controls this.