Abstract: The jackable oil rig employs a leg formed of a plurality of corner columns and transverse stays. Each column is formed of an outer pipe, and inner pipe which defines an annular space with the outer pipe and a hardenable material such as concrete in the space between the pipes. The outer pipe has a constant outer diameter along the length while the inner pipe has a constant outer diameter along the length and an increasing wall thickness from a top section to a bottom section. The wall thickness of the inner pipe may increase step by step from about 30 millimeters in the upper section to about 150 millimeters in the lower section. The construction of the corner column allows oil rigs to operate at ocean depths down to 200 meters.