"The old one they moved aside on Saturday never fitted properly, but this one appears to," he said.
"[But] we have to wait for anything between six hours and two days for BP to complete testing - stress tests or pressure tests - on the well site itself."
Bob Cavnar, a former oil firm executive with 30 years experience in the industry, cautioned that there was still oil flowing from the ruptured well.
"It is good news what they call the capping stack was set on top of the old blow-out preventer about five hours ago, but to be clear it is still leaking the full well stream into the Gulf at this point," he told Al Jazeera on Tuesday.
"The plan we are hearing from BP is that they are going to do what they call a shut in integrity test in the morning.
"What they are going to try to do is to gradually close the well in to see if they can shut it in.
"But the problem is twofold. One is, we all believe there is downhole damage - damage to the casing below the surface of the sea floor. And there is also a problem with weakness in some of the wellhead components.
"So because of that, they are going to have to be very cautious in their shut-in and they will likely have to flow the well to some of the ships overhead."
The latest cap is only meant to be a temporary fix, but if it can withstand the pressure, the leak would be halted, easing the pressure on BP until it can finish drilling a relief well and concrete the site over to permanently stop the flow.
Oil capping efforts
Officials have offered varying estimates for when the relief well will be done, but mid-August is the most common timeframe.
But if the stress tests indicate that the cap will not be able to take the pressure, valves will have to be opened to release some oil into the water, although in much smaller amounts than before.
The new cap was mounted on the well after two days of preparing the site and a day of slowly lowering it into place.
|If cap is unable to take the pressure, valves will have to be opened to release oil [AFP]
The old cap, which was removed on Saturday, was installed on June 4 to capture oil gushing from the bottom of the sea, but because it had to be fitted over a jagged cut in the well pipe, it still allowed crude to escape into the water.
On Monday, BP also hooked up a containment ship to a different part of the leaking well which should be able to start collecting more than 3.8 million litres of oil a day in a couple of days' time, the company said.
The government estimates 5.7 million litres to 9.5 million litres of oil a day are spewing from the well, and the previous cap was collecting about 3.8 million litres of that.
With the new cap and the new containment vessel, the system is expected to be capable of capturing 9.5 million litres to 12.9 million litres - essentially all the leaking oil, officials said.
New ban on drilling
Meanwhile, the US government has issued a new six-month moratorium on deepwater oil drilling in the Gulf of Mexico, replacing an earlier ban that had been struck down by US courts as being too broad.
Ken Salazar, the interior secretary, announced the new drilling ban on Monday that will suspend most deepwater activities, just as the initial plan intended.
|Oil gushed for three days as the old cap was lifted and the new one put in place [Reuters]
The oil industry, caught in a legal tug-of-war, will have to keep its rigs idled in the Gulf of Mexico because of the moratorium which followed the April 20 rig explosion that ruptured the undersea oil well owned by BP.
In an attempt to avoid additional legal challenges, the interior department also said that the new drilling ban – which shuts down 21 rigs - will be based on the type of equipment being used and not solely the depth of the water, as in the first moratorium.
"More than 80 days into the BP oil spill, a pause on deepwater drilling is essential and appropriate to protect communities, coasts, and wildlife from the risks that deepwater drilling currently pose," Salazar said.
Under the agency's revised plan, oil drilling in shallow waters can continue if companies are in compliance with new safety and environmental rules.
Existing deepwater offshore platforms producing oil and gas are not affected by the new order.