Low oil pressure is an indication of worn bearings, broken oil pressure relief valve or a worn or damaged oil pump. Since the oil pressure relief valve usually doesn't go bad and oil pumps usually hold together quite well, it's probably a problem with worn main/rod bearings. If the vehicle has run without an oil change as scheduled on a couple occasions, the bearings probably have too much clearance. If that's the case you might be able to change to a higher viscosity oil and squeeze a few more miles from the engine, but you'll be needing an engine rebuild soon.
