Whilst the aircraft was cruising at FL125 a rapid fluctuation of the right engine oil cooler indicator occurred. The oil quantity indicator of the engine showed 45 l (12 gal) remaining out of a total of 98 l (26 gal). The pilot-in-command headed toward Iloilo reporting to Iloilo tower his difficulty and intention to land there. At FL 80 inbound to Iloilo, the oil warning light flickered. The pilot-in-command immediately pushed the right propeller feathering button, closed the mixture, brought the propeller control aft, but the propeller would not feather. At an altitude of 1500 m (5000 ft) the right engine stopped and the pilot-in-command, being unable to maintain altitude to reach the airport, made a gear up landing on a rice field.