OIL AND GAS ACTIVITY Numerous structures, surface and submerged, sometimes marked by buoys exist in the area indicated. These include drilling rigs which may be temporarily located; details are promulgated by local Navigational Warnings. Production platforms and associated structures, including tanker moorings, storage tankers and platforms on pipelines, generally exhibit Mo(U) lights, aircraft obstruction lights, and audible fog signals. Unauthorised navigation is prohibited within 500 metres of all such structures.