On August 18, 2018, about 2130 Pacific daylight time, a Beech 36, N9031S, was substantially damaged when it was involved in an accident near Washington Regional Airport (KLS), Kelso, Washington. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations (CFR) Part 91 personal flight. The pilot reported that he had filled both fuel tanks the night before the accident; he estimated that he had over three hours of fuel for the cross-country flight the following evening. While en route to the destination airport the engine lost power, which resulted in an off airport landing in a field. A postaccident onsite examination of the airplane by a Federal Aviation Administration inspector revealed that no visible fuel was observed in the right side fuel tank. He then sumped the tank and no fuel was expelled. When he performed a visual inspection of the left side fuel tank, it appeared to be full. The pilot subsequently stated that based on the evidence of the right fuel tank being empty, he probably ran out of fuel. The pilot also mentioned that he could not remember switching fuel tanks. The pilot reported that there were no mechanical anomalies with the engine or airframe that would have precluded normal operation.