Cessna 150 pilot reported landing safely after noting decreasing oil pressure during the flight.

Narrative

Run-up and takeoff; oil pressure normal throughout; approx. 50 PSI; climb out at 2600 RPM. After exiting ZZZ airspace; requested and received VFR flight following from Approach. On west/southwest climbout; noticed small drop in oil pressure; approx. 45 PSI; but still within green arc of gauge. No abnormal engine operations or indications; 2600 RPM. In cruise at 2450 RPM; noticed continued small; slow drop in oil pressure indication; but still within green arc of gauge. No other abnormal engine operations or indications. Gauge indicated at low edge of acceptable pressure. Turn south; oil pressure gauge indicates low oil pressure; approx. 28 PSI. Turned for left downwind ZZZ1 and informed Approach; who [requested handling priority] for me. Landed safely; taxied to FBO; oil pressure indicates approx. 20 PSI during taxi at > 1100 RPM; no other abnormal indications or engine sound/feel. After shutdown; examine fuselage; normal amount of grime noted. Examined engine and inside of cowling; small amount of oil noted at bottom of cowling (less than .1qt approx.). All oil fittings seemed to be clean and tight. Breather tube fittings clean and tight as well.