1999 Mercury Cougar There Oil On Two Spark Plugs Really Bad Compression Making

Oil on the plugs and low comps usually mean broken rings or a hole in the piston, get a leak down test done this will help pin point the problem.

What is a leak down test

This is when you apply a low pressure compressed air into the cylinder at TDC with both valves closed, there is a special tool that screws into the spark plug hole, with the low pressure applied you can determine where the leaks are, such as valves, rings etc.

Can I do the leak down test myself or do I hav to take it to a shop

you need the adaptor a compressor and a regulator to drop the air pressure down, to high a pressure will force the piston down and open a valve this will give you a false reading, if a manual transmission you can put it in gear and pull the hand brake on to help hold the engine at TDC.