What was found
(CAN) DURING REVENUE FLIGHT, ON TAKEOFF, THE OIL PRESSURE WENT TO ZERO ON VR, ROTATION OF THE ACFT. THE CREW COMPLETED THE CLIMBOUT, SHUTDOWN THE ENGINE AND RETURNED TO THE AIRPORT, WHERE AN UNEVENTFUL SINGLE-ENGINE LANDING WAS ACCOMPLISHED. POST-FLIGHT INSPECTION REVEALED NO OIL VISIBLE ON THE OTBD SIGHT GLASS AND BELOW MINIMUM ON THE INBD. TROUBLESHOOTING ONGOING.