NEW ORLEANS — The oil has stopped. For now.
After 85 days and up to 184 million gallons, BP finally gained control over one of America's biggest environmental catastrophes Thursday by placing a carefully fitted cap over a runaway geyser that has been gushing crude into the Gulf of Mexico since early spring.
Though a temporary fix, the accomplishment was greeted with hope, high expectations — and, in many cases along the beleaguered coastline, disbelief. From one Gulf Coast resident came this: "Hallelujah." And from another: "I got to see it to believe it."
If the cap holds, if the sea floor doesn't crack and if the relief wells being prepared are completed successfully, this could be the beginning of the end for the spill. But that's a lot of ifs, and no one was declaring any sort of victory beyond the moment.
The oil stopped flowing at 3:25 p.m. when the last of three valves in the 75-ton cap was slowly throttled shut. That set off a 48-hour watch period in which — much like the hours immediately after a surgery — the patient was in stable, guarded condition and being watched closely for complications.
"It's a great sight," said BP chief operating officer Doug Suttles, who immediately urged caution. The flow, he said, could resume. "It's far from the finish line. ... It's not the time to celebrate."
Nevertheless, one comforting fact stood out: For the first time since an explosion on the Deepwater Horizon oil rig killed 11 workers April 20 and unleashed the spill 5,000 feet beneath the water's surface, no oil was flowing into the gulf.
President Barack Obama, who has encouraged, cajoled and outright ordered BP to stop the leak, called Thursday's development "a positive sign." But Obama, whose political standing has taken a hit because of the spill and accusations of government inaction, cautioned that "we're still in the testing phase."
The worst-case scenario would be if the oil forced down into the bedrock ruptured the seafloor irreparably. Leaks deep in the well bore might also be found, which would mean that oil would continue to flow into the gulf. And there's always the possibility of another explosion, either from too much pressure or from a previously unknown unstable piece of piping.
The drama that unfolded Thursday was a combination of trial, error, technology and luck. As part of what BP calls an "integrity test," a robotic submersible slowly closed a valve on the well's new sealing cap. That choked the flow until the plume, a fixture of cable TV and many a nightmare, disappeared.
BP could nix the test at any moment and reopen the well. Whether the well remains "shut in," to use the industry term, depends on the analysis of pressures in the well. Engineers and scientists hope to see high pressure hold steady during the 48-hour period allotted for the test. That would suggest that the well bore is physically intact. Lower pressure would hint of breaches in the casing and leakage into the surrounding rock.
The initial pressure readings are in an ambiguous range, and officials will have to make a difficult judgment call on whether to keep the well shut in or reopen it, according to Tom Hunter, retired director of the Sandia National Laboratories and a member of the federal government's scientific team overseeing the test.
"If it were a lot higher, it would be an easier decision to make," Hunter said.
Thad Allen, the national incident commander, has said that a pressure reading of 8,000 or 9,000 pounds per square inch would be ideal, while below 6,000 psi might indicate leakage. Hunter, who witnessed the test from BP's war room in Houston, said that the pressure rose to about 6,700 psi and appeared likely to level out "closer to 7,000." He said one possibility is that the reservoir has lost pressure as it has depleted itself.
"We just don't know whether something is leaking or not," Hunter said.
It's not clear yet whether the oil will remain bottled in the cap, or whether BP will choose to use the new device to funnel the crude into four ships on the surface.
For nearly two months, the world's window into the disaster has been through a battery of BP cameras, known as the "spillcam." The constant stream of spewing oil became a fixture on cable TV news and web feeds.
That made it all the more dramatic on Thursday when, suddenly, it was no more.
On the video feed, the violently churning cloud of oil and gas coming out of a narrow tube thinned, and tapered off. Suddenly, there were a few puffs of oil, surrounded by cloudy dispersant that BP was pumping on top. Then there was nothing.
"Finally!" said Renee Brown, a school guidance counselor visiting Pensacola Beach from London, Ky. "Honestly, I'm surprised that they haven't been able to do something sooner, though."
Alabama Gov. Bob Riley's face lit up when he heard the news. "I think a lot of prayers were answered today," he said.
The saga has devastated BP, costing it billions in everything from cleanup to repair efforts to plunging stock prices. Though BP shares have edged upward, they shot higher in the last hour of trading on Wall Street after the company announced the oil had stopped. Shares rose $2.74, or 7.6 percent, to close at $38.92 — still well below the $60.48 they fetched before the rig explosion.
The Gulf Coast has been shaken economically, environmentally and psychologically by the hardships of the past three months. That feeling of being swatted around — by BP, by the government, by fate even — was evident in the wide spectrum of reactions to news of the capping.
"Hallelujah! That's wonderful news," Belinda Griffin, who owns a charter fishing lodge in Lafitte, La., said upon hearing the gusher had stopped. "Now if we can just figure out what to do with all the oil that's in the gulf, we'll be in good shape."
The fishing industry in particular has been buffeted by fallout from the spill. Surveys of oyster grounds in Louisiana showed extensive deaths of the shellfish. Large sections of the Gulf Coast — which accounts for 60 to 70 percent of the oysters eaten in the United States — have been closed to harvesting, which helps explain why one oysterman in Louisiana refused to accept that progress was afoot.
Prove it, said Stephon LaFrance of Burris, La.
"I've been out of work since this happened, right? And I ain't never received nothing from BP since this oil spill happened," he said. "Like they say they stopped this oil leak. I think that's a lie. I got to see it to believe it."
Long after the out-of-control well is finally plugged, oil could still be washing up in marshes and on beaches as tar balls or disc-shaped patties. The sheen will dissolve over time, scientists say, and the slick will convert to another form.
There's also fear that months from now, oil could hitch a ride on the loop current, possibly showing up as tar balls in Miami or North Carolina's Outer Banks.
In Louisiana's Plaquemines Parish, the worst-hit area of the coast, frequent BP and government critic Billy Nungesser, the parish president, offered a word of caution: This whole mess, he said, is far from over.
"We better not let our guard down," Nungesser said. "We better not pull back the troops because, as we know, there's a lot of oil out there, on the surface, beneath it. And I truly believe that we're going to see oil coming ashore for the next couple of years."
The Associated Press and Washington Post contributed to this report.