The pilot of the Piper Cherokee 140 stated that during a short cross country flight he switched from the left to the right fuel tank every 30 minutes. He said that as he approached his destination, the fuel gauges for both tanks indicated that there were approximately 3 gallons of fuel in each wing tank. He said that "he wasn’t concerned about this because he had only 11 miles to go." However, the "engine quit." He said that his fuel selector was on the right fuel tank and showed approximately 2 gallons of fuel. He switched to the left tank which also indicated 2 gallons of fuel. He restarted the engine, but it ran for only approximately 15 seconds. He then prepared for an emergency off field landing. During the emergency landing the airplane collided with a tree. Examination of the airplane by a Federal Aviation Administration (FAA) inspector revealed that both fuel tanks were empty. A cursory examination of the engine revealed no mechanical malfunctions. In a telephone conversation with the pilot, he acknowledged that he "made a mistake by relying on the fuel gauges," and that he "should have planned better."