OCTG Country Tubular Goods are standardized by API, American Petroleum Institute and there are three main types of OCTG tubes, which includes drill pipes, casing pipes and tubing pipes.

Drill pipes are seamless tubes manufactured to transfer drilling torque the entire length of the pipe, often several kilometers.
Casing pipes are tubes used to line the borehole, which is the actual hole dug into the ground to get to the oil.
Tubing pipes are tubes that goes inside the casing pipe, for delivery the oil and gas to the surface.