Car question? I stopped at a gas station to have my oil checked today...?

and the attendant said the oil level was fine but that I had oil on my engine and there has to be a reason why it was there. What could be wrong with my care to cause this?? just wondering before I go to a garage what I might be in for...the car is a 97 Ford Escort that has 150, 000 miles on it. Its been a great car and I would like to keep it going as long as possible unless its needs something crazy expensive. THank you for your opinion.. Oh and btw the car seems to be running fine..