Offshore drilling is rarely carried out in order to explore for petroleum.
When offshore drilling moved into deeper waters of up to 30 metres (98 ft), fixed platform rigs were built, until demands for drilling equipment was needed in the 100 feet (30 m) to 120 metres (390 ft) depth of the Gulf of Mexico, the first jack-up rigs began appearing from specialized offshore drilling contractors
The first offshore drillship was the CUSS 1 developed for the Mohole project to drill into the Earth's crust

