HOUSTON -- The offshore oil and gas industry is launching new rig construction targeting Gulf of Mexico operations, a further sign that activity in the Gulf is returning to conditions before the 2011 Deepwater Horizon oil spill.

This morning, Diamond Offshore Drilling Inc., an oilfield services company specializing in mid- and deepwater equipment, announced that it will build a new semisubmersible rig at a south Texas shipyard, to be delivered in the second half of 2013. A Diamond subsidiary has commissioned the Keppel AmFELS shipyard in Brownsville to construct the rig.

The company says no new rigs of this type are currently under construction. The moored semisubmersible will be capable of operating in water depths of up to 6,000 feet and will have enough quarters to house a crew of 140 workers.

The new rig, to be named Ocean Onyx, will cost about $300 million to build. The price tag and timeline for construction will be about half that of what the industry could normally expect because the shipyard will use the hull from Diamond's decommissioned Ocean Voyager rig.

Diamond is currently building three new drillships designed for ultra-deepwater operations, to be added to its existing fleet of just one drillship once construction on those is completed. In a release, company CEO Larry Dickerson said emerging demand for offshore technology in the Gulf of Mexico and elsewhere makes all three projects good investments.

"No new capacity targeting the standard midwater and deepwater markets is currently under construction, and this [Ocean Onyx] rig should be ideally suited to meet emerging demand in this segment," said Dickerson. "When added to our three ultra-deepwater drillships under construction, this unit will continue the process of renewing Diamond's fleet."

Diamond was also careful to note that the new Ocean Onyx will be equipped with a "five-ram blowout preventer," mindful of government and public scrutiny of the safety of offshore oil and gas exploration as companies continue to add operations in deeper and more remote locales.

Diamond says it now operates a fleet of one drillship, 32 semisubmersible rigs for deepwater and 13 jack-up rigs used mainly for shallower offshore drilling.

In its periodic international rig count released today, Houston oilfield contractor Baker Hughes Inc. said that the global fleet of offshore rigs stood at 342 individual vessels at the end of the year, up from 329 at the close of 2010. Two offshore rigs were added to the fleet in December.

The global total of land rigs rose from 2,898 at the end of 2010 to 3,270 counted in December of last year.