Prior to departure the pilot had calculated that there was sufficient fuel onboard for the flight. About 11km from Alice Springs aerodrome, with the left tank selected, the engine failed. The pilot selected the right tank, the engine restarted and the flight continued towards the field. Shortly after the aircraft entered downwind for runway 06 at 3200 feet, about 4km from the aerodrome, the engine failed again. The pilot advised the tower controller that the aircraft "was out of fuel" and was cleared to land as required. After the aircraft landed safely on runway 24, the pilot visually checked the tanks. The right tank appeared empty but there was 30-40 mm depth of fuel in the left tank. The left tank was selected and the engine started normally, the aircraft was then taxied to the parking area. When the aircraft was refuelled 156 litres of fuel was added to the right tank and 122 litres to the left tank. Each tank holds 150 litres of useable fuel. All the fuel drains were checked by an engineer and were contaminated by dirt and water.