No clue as to the car you have. But cars with a PVC valve that fails can cause this. It the breather tube form the valve covers to the intake. Cars that have a PCV valve can pull in a little oil and the valve wears out. I have seen cases where so much oil is pulled in that it just sits at the bottom of the intake as a pool.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car