In a written report, the pilot stated that he was in contact with the Camarillo Airport (CMA) air traffic control tower, descending on a 5-mile final approach for the runway, when the airplane experienced a total loss of engine power. He stated that there were no "abnormal" indications on the engine gauges, and he believed he had exhausted all useable fuel in the two right wing fuel tanks. He immediately switched the fuel selector to the left wing tank. The engine did not regain power, so the pilot verified that the magneto switches were on. According to the pilot, there is no electric starter installed for the engine. The airplane continued to descend, and about 500 feet above the ground, the propeller stopped rotating. The pilot released the banner he was towing, and he made a forced landing in a rough field about 1442. The airplane nosed over during the landing rollout, and the left wing's structure was damaged. The pilot reported that the airplane was equipped with three fuel tanks, two in the right wing and one in the left wing. Each tank holds 18 gallons of fuel, for a total of 54 gallons. During banner tow operations the fuel burn off rate is about 8 gallons per hour. All fuel tanks were filled to capacity prior to the pilot's 1040 takeoff. At the nominal engine power setting the pilot indicated he typically uses, the airplane's endurance is about 6 hours. In the pilot's completed "Pilot/Operator Aircraft Accident" report he wrote that the accident would have been prevented if he had switched to the left fuel tank before the right tanks ran out of fuel.