Platform supply vessel (often abbreviated as PSV) is a ship specially designed to supply offshore oil platforms. These ships range from 65 to 350 feet in length and accomplish a variety of tasks. The primary function for most of these vessels is transportation of goods and personnel to and from the offshore oil platforms. The cargos are as diverse as the tasks that they accomplish. Drilling mud, pulverized cement, diesel fuel, potable and non-potable water, and chemicals used in the drilling process make most of the below decks cargo. Common and specialty tools are carried on the large decks of these vessels. Most carry a combination of above and below deck cargoes, allowing for the stability of the vessel. Some of these ships are constructed (or re-configured) to accomplish a particular job. This could include deploying, monitoring, and retreiving siesmic cable for mapping geologic formations that may possibly hold hydrocarbons. Other vessels are equipped with tools, chemicals and personnel to "work-over" existing oil wells for the purpose of increasing the wells' production. Many other specialty jobs are regularly accomplished every day in the oilfields of the world.
Crews on the smaller ships can number as few as three or four. Some of the larger vessels carry 20 to 30 people, as many as half of them could be crew, the remainder being specialist such as scientist, geologists, or people involved in any of the many jobs related to operations on the oil rig.