NEW ORLEANS – BP finally choked off the flow of oil into the Gulf of Mexico on Thursday — 85 days and up to 184 million gallons after the crisis unfolded — then began a tense 48 hours of watching to see whether the capped well would hold or blow a new leak.

To the relief of millions of people along the Gulf Coast, the big, billowing brown cloud of crude at the bottom of the sea disappeared from the underwater video feed for the first time since the disaster began in April, as BP closed the last of three openings in the 75-ton cap lowered onto the well earlier this week.

"Finally!" said Renee Brown, a school guidance counselor visiting Pensacola Beach, Fla., from London, Ky. "Honestly, I'm surprised that they haven't been able to do something sooner, though."

But the company stopped far short of declaring victory over the biggest offshore oil spill in U.S. history and one of the nation's worst environmental disasters, a catastrophe that has killed wildlife and threatened the livelihoods of fishermen, restaurateurs and oil industry workers from Texas to Florida.

Now begins a waiting period during which engineers will monitor pressure gauges and watch for signs of leaks elsewhere in the well. In the worst-case scenario, pressure from the rising oil could fracture the well and cause leaks to erupt across an area of the seafloor too large to cap.

If engineers see any sign of a new leak, the cap will be reopened, allowing oil to spill into the sea again.

Even if the well holds out for the whole two days, the vents will be opened again and oil released while engineers conduct a seismic survey of the ocean floor to make sure oil and gas aren't breaking out of the well into the bedrock, said retired Coast Guard Adm. Thad Allen, the Obama administration's point man on the disaster.

"For the people living on the Gulf, I'm certainly not going to guess their emotions," BP vice president Kent Wells said. "I hope they're encouraged there's no oil going into the Gulf of Mexico. But we have to be careful. Depending on what the test shows us, we may need to open this well back up."

Either way, the cap is only a temporary fix until a relief well can be drilled into the bedrock and cement and mud can be pumped into the broken well deep underground, creating a seal that will hold more securely. BP expects to complete a relief well by mid-August, and perhaps as early as the end of this month.

Source: Long, Colleen, and Harry R. Weber. "BP chokes off the oil leak; now begins the wait." Associated Press Writers (2010): n. pag. Web. 15 Jul 2010. <http://news.yahoo.com/s/ap/20100715/ap_on_bi_ge/us_gulf_oil_spill>.