As @nytryder26 already said, we'll need to see what you see in order to get an idea about what issue you're having. That will also help us try and figure out where the oil is coming from, which will determine what kind of fix is appropriate.
Off the top of my head, two possibilities come to mind. First would be a valve cover gasket leak if the oil is coming out from around the top of the cylinder head; the obvious solution to that would be to replace the valve cover gasket.
Other than that, the next most common cause for oil to appear on the top of the engine would be from excessive crankcase pressure blowing oil back out the fill cap, PCV valve or other vacuum connections. High crankcase pressure usually results from either piston rings that are shot and no longer able to contain cylinder compression, or a leaking head gasket. Obviously the fixes for these kind of issues are going to be a lot more difficult and expensive.
But add some pictures so we have something to go on; these are just conjectures of things that could cause the appearance of oil and may or may not have anything to do with your actual problem.