The pilot gave a 'mayday' call advising that the aircraft had suffered an engine failure, and that he would be carrying out a forced landing. The aircraft was landed in a swampy area between trees which damaged both wings during the landing roll. The pilot stated that he had not visually checked the fuel contents or the security of the caps and access covers before departing Darwin as he had filled the right tank before the previous flight. The fuel gauges did not indicate the expected amount of fuel even after the aircraft was established in cruise but the pilot elected to continue to his destination. About 6 km from the destination, with the left hand tank selected, the engine stopped. The pilot switched to the right tank but the engine did not restart. It is possible that the right tank was losing fuel from a faulty venting system on the flight into Darwin.