Cobalt International Energy has declared a force majeure under its drilling contract with Diamond Offshore Company for the Ocean Monarch drilling rig.

Cobalt was to use the Ocean Monarch rig to begin drilling operations at the North Platte 1 exploratory well in the Gulf of Mexico.

The move by the company is a result of the ban on offshore drilling activity following the explosion of the Deepwater Horizon rig in April and the subsequent oil spill in the Gulf of Mexico.

Cobalt said the offshore drilling ban will defer its drilling programme in the Gulf of Mexico by six months and will cost the company about $15m.