C172 pilot reported loss of oil pressure on initial climb and return to departure airport.

Narrative

Got to the ZZZ on the morning of Day 0 getting ready for a flight to ZZZ1. Preflight went well and aircraft was ready to fly. Engine had about 6 quarts of oil. We started the engine and did the usual. We taxied out to the run-up area west of runway XX and conducted the run-up. Engine performed normal and oil pressure was in the green as well as the oil temperature. We were holding short of RWY XY as we performed our pre-takeoff checklist and briefing. I made our call to let other pilots aware that we were departing RWY XY. I pulled on to RWY XY and lined up with the centerline; held the brakes; applied full power and once again engine is running smooth and gauges are all in the green. We continue our takeoff on a straight out departure and at about 500 FT I look at our oil pressure and we are losing oil pressure significantly. Continually; I enter a left bank and enter a left base for RWY XZ and I make my call once again letting everybody know that I was joining a left base for XZ and that I had no oil pressure. I continue and we land RWY XZ get off the runway shutdown and there was oil all over the left side of the fuselage. We push back and I check the oil dip stick and there was not a single drip of oil. Tied up; and left.