oil pump??
2 Answers
Could just be the oil sending unit going bad and sending wrong signals to the dash gauge
http://www.amazon.com/ACDelco-D1834A-Original-Equipment-Pressure/dp/B000C9P3E2/ref=sr_1_1?ie=UTF8&qid=1418413980&sr=8-1&keywords=ACDELCO+Part+%23+D1834A&pebp=1418413984179 and procedure http://www.ehow.com/how_6056584_remove-oil-pressure-switch-oldsmobile.html