The pilot reported that he had added a specified amount of fuel at the previous fuel stop and he was using a fuel totalizer to determine the quantity of fuel on-board. After climbing to a cruise altitude of 14,000 feet above ground level he discovered that the fuel mixture control was frozen and he was unable to lean the mixture to a lower fuel flow setting. The pilot reported that because of the increased fuel consumption he briefly considered an enroute stop for additional fuel but decided to continue. During descent the airplane experienced a complete loss of power in both engines and the pilot made an emergency off-field gear-up landing about 7 miles from the destination. The airplane impacted terrain and thick scrub trees which resulted in substantial damage to both wings, both engine mounts, and the fuselage. A postaccident examination found that only a trace of fuel remained. The pilot also reported that there was no mechanical malfunction or failure and that his inadequate fuel management was partly because he had become overconfident in his abilities after 50 years of flying.