Jack-up, submersible, and semi-submersible vessels are types of:

Jack-up, submersible, and semi-submersible vessels are classified as mobile offshore drilling units (MODUs) because these types of vessels are specifically designed for offshore drilling operations. Each type of vessel has unique characteristics that make it suitable for various environmental conditions and drilling requirements.

Jack-up rigs consist of a floating hull that is equipped with extendable legs that can be lowered to the seabed, providing stability in shallow waters. Submersible units are designed to float on the surface but can be submerged to a certain depth for stability, usually in deeper waters. Semi-submersible units, similar to submersibles, float on the surface but remain partially submerged, offering resistance to waves and providing stability for drilling operations in rough seas.

In contrast, tanker ships are primarily designed for transporting liquids, cargo ships are meant for carrying cargo, and fishing vessels are dedicated to catching fish. These categories do not encompass the specialized design and function of mobile offshore drilling units. Therefore, the identification of Jack-up, submersible, and semi-submersible vessels as types of mobile offshore drilling units accurately reflects their intended use in the petroleum extraction industry.