The pilot flew four skydiving flights without refueling. On the last flight, after the skydivers exited the airplane, the pilot initiated a descent and the airplane experienced a total loss of engine power. The pilot knew he could not make it back to the airport and made a forced landing to a gravel area. The airplane collided with a gravel mound and nosed over resulting in substantial damage to the airframe. According to the pilot, the airplane owner assisted him in fueling the airplane from a local fuel truck. The pilot said he used a ladder and started refueling the right wing with the owner manning the pump. While they were refueling the airplane, the owner asked the pilot if he was getting any fuel because the fuel meter was not running. They looked at the airplane's right main fuel tank and it appeared to be full. The pilot then added what he believed to be 10 gallons of fuel to the left main fuel tank. The pilot thought he had 37.5 gallons of fuel on board when he departed. Examination of the wreckage did not reveal any preimpact mechanical malfunctions, nor did the pilot report any. The examination also did not reveal any evidence of usable fuel. Additionally, examination of the airplane rubberized bladder type fuel cells located on the inboard bay of each wing panel revealed the snap fasteners normally used to prevent the collapse of the flexible cells were not installed and wrinkling of the bladder was noted. The fuel bladders were replaced about 5 years prior to the accident. It is possible that due to the wrinkling of the right fuel bladder, the pilot may not have had the fuel that he expected when the tank was topped off.