What was found
(CAN) THE AIRCRAFT DEPARTED WITH ALL INDICATIONS NORMAL. THE FLIGHT CREW TOOK OFF, LEVELED AT 3000 FEET, THEN WAS CLEARED TO 13,000 FT. 4 MINUTES INTO THE FLIGHT PASSING 5000 FEET, CREW GOT AN RED OIL PRESSURE LIGHT, CHECKED THE OIL GAUGE WHICH WAS AT ZERO PSI. THEY THEN SHUT THE ENGINE DOWN AND RETURNED TO THE FIELD LANDING SINGLE ENGINE.