The aircraft operator employed two Navajo aircraft on regular crew changes at oil exploration sites. On the previous day one of these aircraft had become unserviceable at Cunnamulla. The operator had then hired VH-EDL to pick up the next day's work. This aircraft was to be flown to Cunnamulla by an engineer who would repair the faulty aircraft and return to Archerfield in that aircraft. One of the operator's pilots would then accept the replacement aircraft and continue the charter to Jackson. This pilot had not flown the replacement aircraft previously. At Cunnamulla, the two pilots discussed the fuel quantity in VH-EDL which they agreed was adequate for the flight to Jackson. The fuel quantity could not be checked visually, due to wing dihedral. The aircraft was not fuelled at Cunnamulla as indicated on the flight plan. During the flight to Jackson the pilot became increasingly concerned about the fuel state of the aircraft. He selected the auxiliary tanks but noticed that the gauges were indicating empty and assumed that these tanks were empty. The pilot then reselected the main tanks as his employer did not favour allowing the tanks to be run dry due to passenger considerations. The pilot considered diverting to an alternate strip but decided to continue to Jackson. At about 1400 feet above ground level and three kilometres from the Jackson strip the left engine began to surge and then stopped. Shortly afterwards, the other engine stopped. The pilot elected to land the aircraft in an area of river channels. During the landing, the aircraft struck trees and ran through a washout. Investigation revealed that the outboard tanks contained between 28 and 30 litres of fuel and that the inboard tanks were dry. No evidence of fuel leakage was found. Fuel-use calculations indicated that the aircraft was actually flown further than would be expected using the aircraft manufacturer's data, and that the pilot who had normally flown the aircraft was not making adequate allowance for fuel burn during flights. The fuel gauges could not be calibrated after the accident.