What was found
NINE MINUTES INTO THE FLIGHT, NR 1 ENGINE OIL PRESSURE READ ZERO (PRESSURE WAS NORMAL PRIOR TO TAKEOFF). NO CAPTION LIGHTS ILLUMINATED AND TEMPERATURE WAS WIT HIN NORMAL OPERATING RANGE. RETURNED TO SUPERIOR AND LANDED. DURING COOL DOWN, OIL PRESSURE SLOWLY RETURNED TO NORMAL RANGE. PROBLEM NEVER RECURRED. SUSPECT LOOSE WIRE POSSIBLY AS A RESULT OF MECHANIC WIPING DOWN ENGINE DECK EARLIER IN THE DAY.