Years of research and planning have brought the oil giant to this point, and to this solitary location about 190 miles southeast of Houston, where water depths reach nearly 7,000 feet and a vast, uninterrupted expanse of sea is the only view.

Now, the only thing left to do is wait, as a drill bit far below inches closer to a target that may or may not exist.

“You can do all the planning you want,” said Tom Jones, drilling superintendent of Chevron's Moccasin prospect, aboard the new rig called the Discoverer Inspiration. “But there's only one way to find out, and that's to drill a well.”

The fact that one of the world's biggest oil companies has found itself here underscores how difficult the global hunt for oil has become. It also helps explain why the Gulf of Mexico has recently taken on greater importance in that search.

As oil companies face limited access to new reserves elsewhere around the world, the heavily explored U.S. basin — with its established oil and natural gas infrastructure and stable fiscal regime — has grown more attractive. Recent deepwater discoveries there have also brought new attention to the region, while improved drilling rigs and other technologies have put fields into play that once weren't feasible to explore and develop.

“(Oil companies) understand the financial risk in the Gulf of Mexico and are a whole lot more comfortable with that than some of the other areas they might consider going to work,” said Steven Newman, CEO of drilling contractor Transocean Ltd., owner of the Discoverer Inspiration, with headquarters in Zug, Switzerland, and large operations in Houston.

Others on board

BP, the largest oil and gas producer in the Gulf, recently relocated its global exploration and production business to Houston from Europe as it eyes growth in the U.S. offshore area.

Royal Dutch Shell says in coming years, its Upstream Americas unit, which oversees oil and gas exploration and production activities in North and South America, has the opportunity to attract up to 40 percent of the European company's global upstream budget, up from 25 percent in 2005, partly for projects in the Gulf of Mexico.

Elsewhere, Houston's Marathon Oil said in February it plans to spend $370 million this year on exploration wells in the deepwater Gulf of Mexico, more than double what it spent in 2009. And more state-owned oil companies are either entering the region for the first time or making expansion plans.

For Chevron, the deepwater Gulf of Mexico is the largest of four geographic focus areas for the company. As such, it receives “more than its fair share” of company resources — of the $17.3 billion the company will spend in 2010 on its upstream oil and gas exploration and production budget, $4.1 billion will go to the U.S., including the Gulf of Mexico, and will for the next five to 10 years, said Gary Luquette, president of Chevron's North America Exploration and Production Co. in Houston.

“I've heard the term used, a resurgence in the deepwater Gulf of Mexico. But for us, this has been a constant purpose now for nearly a decade,” Luquette said.

And President Barack Obama's new plan to open more U.S. waters to drilling in the coming years, including parts of the eastern Gulf of Mexico and Atlantic coast, will allow Chevron to sustain investments in the Gulf of Mexico beyond what it is planning today, he said.

The sweet spot

Major oil companies have focused particular attention on an ancient rock bed geologists call the Lower Tertiary trend, which runs miles below the sea floor in an outer rim of the U.S. Gulf between Texas and Louisiana.

Thought to be the biggest U.S. oil discovery in generations, Lower Tertiary fields are expected to help offset declines in shallow water fields and lift overall output of the Gulf of Mexico, which today accounts for about a quarter of U.S. oil production.

But the region also presents huge technical and cost challenges.

Not only are fields often found in waters 2 miles deep, but oil and gas deposits, buried under think salt layers, are hard to detect in geologic surveys. Also, extreme temperatures and pressures in reservoirs test equipment.

Last month, Shell became the first to begin commercial production of oil from Lower Tertiary fields at its new $3 billion Perdido hub.

Over time, 15 of the 19 discoveries made so far in the region have the potential to be big enough to warrant commercial development, estimates Leta K. Smith , director of IHS-Cambridge Energy Research Associates ' E&P Trends Forum in Houston.

“It represents a big opportunity, particularly for the larger oil companies, because they're the only ones that can afford that kind of risk,” she said.

The industry's success rate in the deepwater Gulf of Mexico is roughly one discovery for every three exploratory wells drilled, she said, although others peg it closer to one in eight.

Either way, the odds of coming up empty remain frighteningly high, as do the consequences: Each dry hole is estimated to cost at least $100 million.

Steering drill's path

Last year, Chevron racked up four misses in the deepwater Gulf but also celebrated the huge Buckskin discovery, in an area known as Keathley Canyon, that will help cover outlays for the dry holes.

The Moccasin well Chevron is drilling today is about five miles southeast of the Buckskin. The plan calls for a well drilled to a total depth of 29,000 feet — which includes the 6,750 feet of water between the ship and the sea floor.

On a recent visit to the Discoverer Inspiration, drilling operators were about a third of the way to the target. A geologist on board analyzed rock and salt “cuttings” returned to the surface for clues about what the formation may hold.

If need be, engineers, armed with real-time well data, can recommend small adjustments to the path of the drill bit, which operators can make with joysticks from a control room on the ship.

But they can only “see” where the bit is now. Chevron, despite the millions spent getting to this point, still remains blind to what's ahead.

“Exploration is what it is,” said Jones, the drilling superintendent. “It's a shot in the dark.”

brett.clanton@chron.com