Abstract: Employee #1 was standing between a derrick and a wellhead to help line up an oil well servicing derrick that was backing up to a well to set up and pull the pump for servicing. When an observer signaled the derrick driver to back up, the driver shifted into reverse and slowly rolled back, then suddenly accelerated. Employee #1 was pinned between the derrick and the wellhead and died of his injuries. The results of the investigation indicated driver's error because the driver mistook the accelerator for the brake when he was backing up the rig. The observer had initially given his hand signals from the driver's side of the rig but, immediately before the accident, he had moved to the opposite side. This change in position may also have contributed to the driver's error.