The stringent maintenance requirements that apply to North Sea structures make the cost of inspection a significant factor in North Sea operations. A failure on a large production platform necessitating its shut down would result in a loss of revenue of between half and three-quarters of a million pounds per day. Current practice is such that the whole inspection process is very weather-dependent, and only a portion of a large structure can be examined during the ‘weather window’ (roughly speaking, the period between April and October). The area to be inspected has to be planned in advance, acoustic nets have t o be laid down and calibrated, a range of sophisticated equipment has to be deployed; divers also require relatively long lead times prior to the operation and considerable time for decompressing after the operation. The use of divers will, it is hoped, diminish. It is now general practice to use Remotely Controlled Vehicles (RCV) and television for sub-sea inspection.