I've seen oil in such a manner in many v-6 and v-8 engines due to faulty intake manifold gaskets, faulty valve guide seals, and defective piston rings in the affected cylinder. If you're having problems finding the cause, have a qualified repair shop check it for you, then decide if you want to proceed with the repairs.
You also need to check some of the areas such as the valve cover, oil pan, oil filter or the oil filter cap. To inspect the areas, you need to wipe the oil on the surfaces so that you may be able to check the exact point that is leaking. You need to contact a mechanic for advice. Read http://www.ehow.com/list_7649826_causes-engine-oil-leaks.html to help you diagnose the problem.