Abstract: A self-propelled crawler/tractor apparatus is disclosed for traveling through a tubular pipeline while conducting pipeline wall inspection operations and/or towing gear for cleaning, maintenance and the like. The crawler/tractor apparatus is propelled by a plurality of radially positioned motorized traction wheels. Each motorized traction wheel includes a brushless DC electric motor along with clutch, gearbox and other mechanical drive components integrated into a compact self-contained motorized wheel assembly which is sealed and filled with an electrically non-conductive lubricating/cooling oil. The seal integrity at each wheel assembly is maintained against oil leakage and debris ingress by a pressure-balancing mechanism which matches internal oil pressure to the exterior ambient pressure present in the pipeline. The electric motor drive for each traction wheel is individually controlled via an onboard computer to provide a wide range of torque and wheel speeds.