gas in engine oil
 

check engine light came on, running rough, problem is oxygen sensor - checked the oil level, and I smelled gas on the dipstick. What is the cause and cure

If way too much gas goes into the combustion chambers, it can leak past the rings into the oil. Gasoline is not a very good lubricant for the motor parts, so you should change the oil before driving it. A bad O2 sensor can make the mixture go rich, though it could also be triggering a warning because it is detecting such a huge amount of fuel.

A number of possible causes; if you don't find anything unplugged or any obvious damage it may be best to take the car to a specialist.

Note that generic code readers will not see all the possible codes; there are some that are BMW/MINI specific and you need one of their code readers to see them.

--DD