HOUSTON -- Chevron Corp. says it is using an advanced drillship in the deep waters of the Gulf of Mexico that boasts new technology that the company says will make offshore oil and gas exploration safer.

Yesterday the company announced that the new ship, Pacific Santa Ana, built according to Chevron's designs, had entered the Gulf. The ship will be used to explore for oil and gas deposits beneath the waves under a five-year contract between Chevron and an arm of the offshore equipment contractor Pacific Drilling SA. It will be the fifth drillship Chevron will use in its Gulf exploration program, according to the company.

The new vessel will be the first in the world to house "dual gradient drilling" technology, which "has the potential to change the way deepwater wells are drilled," Chevron Vice Chairman George Kirkland said in a release.

Dual gradient drilling differs from traditional deepwater drilling, the company said, because it employs two different weights of drilling fluid rather than the single fluid normally used in the borehole. The offshore energy industry uses the fluid, or mud, to control well pressure but also to control temperature, take technical readings of the well and carry well cuttings out of the hole to the surface.

Drillers will use a separate fluid weight in the riser above the seabed in tandem with the subsurface fluid used in the process. The design "effectively eliminates water depth as a consideration in well design," Chevron says, which suggests the technique could be used to explore ever farther offshore into deepwater columns.

Company officials say using two separate fluid weights lets drillers better match the natural pressure acting against the equipment that could lead to a well blowout should offshore workers fail to control it.

The dual gradient drilling capability should allow ship workers to notice changes in pressures and respond more quickly and accurately, Chevron says. The company said the Pacific Santa Ana still needs to be fitted with some drilling equipment before it can start work, but it added that the ship already holds the new and advanced dual gradient drilling riser and 72,000 feet of cable for the new system, along with six mud pumps and "extensive fluid management systems enhancements."

Pacific Drilling says its new ship can drill at water depths of 12,000 feet and can drill to a vertical depth of 40,000 feet. It holds a dual derrick system, can carry 19,000 barrels of drilling mud and has room to accommodate 200 workers.

That firm says that four of its drillships are in active service and that it has commissioned Samsung Heavy Industries Co. to build two more, both scheduled for delivery next year.

According to Pacific Drilling's fleet status report, Chevron is paying a contractual day rate of about $467,000 to use the ship and crew. Three of its other ships are drilling off the coasts of Nigeria and Brazil.