Abstract: A large scale hydraulically driven downhole reciprocating tractor to display substantially continuous advancement. The tractor may be configured to pull coiled tubing downhole in a continuous manner so as to substantially avoid static frictional resistance to the pulling. As a result, the tractor and coiled tubing may achieve up to about twice the depth into the well otherwise attainable. Additionally, the tractor may include a fail safe mechanism whereby a plurality of pilot operated valves are employed to ensure that immobilization of at least one anchor of the tractor is present at all times during downhole advancement to thereby avoid the undesired effects of coiled tubing spring-back.