British Petroleum engineers have started the "static kill" procedure meant to plug the Gulf Coast oil spill for good.
Tuesday afternoon, crews began pumping mud down the faulty well, hoping to seal the rig from the top.
Pressure in the well dropped quickly in the first 90 minutes of the process-- a sign that everything was going as planned, BP said.
Site leader Bobby Bolton added that the work could be complete by Tuesday night or Wednesday, though engineers won't know for more than a week if it the well is plugged for good.
Tests were done early Tuesday by probing the busted blowout preventer with an oil-like substance to determine whether it could withstand the static kill process.
The test was originally scheduled for Monday, but the discovery of a small leak in the well's cap forced crews to delay the operation until Tuesday.
"During final preparations to commence with the injectivity test, a small hydraulic leak was discovered in the capping stack hydraulic control system," BP said in a statement.
"This is a really positive step forward," Allen said. "It's going to be good news in a time where that hasn't been very much good news, but it shouldn't be a cause for premature celebration."
New BP CEO Tours Gulf
BP began drilling the primary 18,000-foot relief well May 2, 12 days after the Deepwater Horizon rig exploded and killed 11 workers. The well is now only about 100 feet from the target and BP PLC Senior Vice President Kent Wells said it could reach its desired point by Aug. 11.
BP's incoming CEO Doug Suttles took boat and beach tours over the weekend weekend for a closer look at progress on the well.
To prove recovery was moving in the right direction, federal agencies recently reopened several fishing regions in the Gulf, which Suttles supported.
"They're not going to open these waters to either sport fishing or commercial fishing if it's not safe to eat the fish," he said. "I would eat their food -- the seafood out of the Gulf here-- and I would feed it to my family."
Still, many are wondering where the millions of gallons of oil already in the Gulf has gone. Little appears on the surface of the water, but a short boat ride into the Louisiana marshes reveals thick, black oil.
"When the Coast Guard takes people on the flight and says there is no oil out there and we come out an hour later and there're pictures of oil all over -- what does that tell you?" Plaquemines Parish President Billy Nungesser asked.
What's also unclear is whether the chemical dispersants used to break up the oil will affect marine life. One congressman has described the dispersants as "carpet bombing" the Gulf.
Still, BP insists the chemicals were approved by the Environmental Protection Agency.