New Orleans, Louisiana (CNN) -- BP says it has placed a new containment cap on its crippled well in the Gulf of Mexico that's been gushing oil since an explosion and fire April 20.

The company hopes the new cap will be able to completely contain the leaking oil, but tests are still needed to determine its effectiveness.

Video supplied by BP showed robotic arms gingerly lowering the new 18-foot, 150,000-pound cap over the well.

For now, some oil continues to gush from the upper section of the new cap. That was expected and will continue until BP begins "well integrity tests" Tuesday, BP said. The process could take anywhere from six hours to two days.

If the new cap does not completely contain oil from the crippled well, some may have to be brought to the surface to waiting containment ships. But under a worst-case scenario, there could be new damage to blowout preventer.

BP said in a statement Monday night that, "It is expected, although cannot be assured, that no oil will be released to the ocean for the duration of the test. This will not however be an indication that flow from the well bore has been permanently stopped."

It said information gathered during the test will be reviewed with relevant government agencies. The company said it's possible the tests might be extended even further.

Retired Coast Guard Adm. Thad Allen, the man in charge of the federal response, said Monday scientists will be checking the pressure inside the well, and then determining whether the cap is holding the oil in or if crews will need to continue siphoning oil.

A critical step is making sure there's no hydrate buildup, according to BP Chief Operating Officer Doug Suttles.

In the best-case scenario, the containment cap would have the ability to close down the valves and slowly contain all the oil, Allen said.

But if oil collection were still necessary, over the next two to three weeks, 60,000 to 80,000 barrels (2.52 million to 3.36 million gallons) a day could be collected as part of the containment process, according to BP Senior Vice President Kent Wells. That's because the new containment cap would eventually allow four collection ships to access the well, rather than the maximum of three allowed by the old cap, Allen said earlier.

While robots worked to replace the old cap, crude oil continued to leak out. Scientists estimate that 35,000 to 60,000 barrels of oil have spewed daily from BP's breached well.

Now, even if oil does have to be sent to the surface, BP said it has more resources at its disposal. The oil-gathering ship, the Helix Producer, was put in place Monday to recover oil, joining the Q4000, which is already active.

Between the two ships, crews should be able to collect up to 33,000 barrels of oil per day, Suttles said.

Meanwhile, as efforts to place the containment cap on the well were unfolding, the U.S. Interior Department said Monday it is issuing a new moratorium order in a second effort to block deepwater oil and natural gas projects.

But the was opposition from a key Democratic senator and even some drilling companies that limit their activities close to shore.

The government said the new moratorium is to "protect communities, coasts, and wildlife" while oil and gas companies implement safety measures to reduce the risks of blowouts and oil spills associated with deepwater drilling. The ban will be in effect through November 30, 2010, or until Interior Secretary Ken Salazar determines that deepwater drilling operations can proceed safely.

It would prevent further deepwater drilling in the Gulf of Mexico until officials determine what went wrong in the April 20 explosion and fire at an oil rig that led to oil gushing into the ocean 5,000 feet below the surface.

A previous six-month ban issued in the wake of the Gulf oil disaster was thrown out by a federal judge in New Orleans. Last week, a federal appeals panel rejected the government's request to overturn the lower court judge's decision. The new Interior Department order supersedes the old one.

"More than eighty 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 in a statement. "I am basing my decision on evidence that grows every day of the industry's inability in the deepwater to contain a catastrophic blowout, respond to an oil spill, and to operate safely."

He added, "I remain open to modifying the new deepwater drilling suspensions based on new information."

But Democratic Sen. Mary Landrieu of Louisiana called the moratorium "unnecessary, ill-conceived and a second economic disaster for the Gulf Coast."

She spoke before a presidential commission, tasked with reviewing the response to the oil spill and making recommendations about the future of offshore drilling. Landrieu called the BP oil spill the "exception instead of the rule" and said the deepwater drilling moratorium will kill jobs. The National Oil Spill Commission is holding meetings in New Orleans Monday and Tuesday.

"Whether you call it a moratorium, a suspension or a pause, the result will still be a substantial loss of jobs," Landrieu said. "Even the revised moratorium will force thousands of hard working Louisianians and others in the Gulf Coast to the unemployment line. So I strongly urge this commission to take a quick and decisive action to immediately lift moratorium to save our business and our economy."

Cherri Foytlin, whose husband works for a firm that supplies tools to drilling companies, agreed.

"What I want the commission to walk away with is that we are people down here, and the moratorium and the oil spill affects people and not just big companies. When you rage against big oil like BP and Exxon, you're really raging against me," she said.

Shallow water drilling activities can continue to move forward, under the Interior Department's order, if operators comply with all safety and environmental requirements. The department said that's because they don't present the same type or level of risks that deepwater drilling operations can, it said.

But some concerns are being expressed even by firms that limit their drilling activities to shallow water.

Randy Stilley, president and chief executive officer of Seahawk Drilling, said in a statement that while shallow water drilling supposedly is being allowed under the new order, "the reality is that permits for shallow water drilling are not proceeding despite the widespread efforts being made by the industry to honor the letter and spirit of new Interior regulatory standards." Jim Noe, senior vice president and general Counsel of Hercules Offshore, added, "To date, and despite assurances from the White House and the Interior Department, about one-third of the shallow water fleet has been idled by the application of what can only be called a de facto moratorium."

As efforts continued Monday to get the new cap in place, Allen and BP executives emphasized that work was also continuing on two relief wells, which he called "the final solution" to shutting down the leaking well.

The first relief well is now five feet away from the main well and, at 17,840 feet deep, it's 30 feet above the hoped-for final casing point, BP's Suttles said Monday. That's where BP will run additional tests, then aim for the final intersection point. Given the closeness to the target, he said that BP was estimating "kill" operations to shut down the main well could take place at the end of the month.

The second relief well, which has been drilled as a redundancy measure at the behest of the Obama administration, is now at 15,874 feet deep, Suttles said. He added that BP is going to stop drilling that well farther unless it ends up being needed.

"If the relief wells for whatever reason happen to fail, the other option we are working on how do we install what I will call a permanent collection system, which is where we're working on pipelines to other facilities," BP's senior vice president, Kent Wells, told the National Oil Spill Commission on Monday.

While response crews were hard at work over the weekend, seven members of the National Oil Spill Commission visited different areas of the Gulf Coast affected by the oil disaster ahead of their meetings in New Orleans. Committee co-chairman William K. Reilly, a former Environmental Protection Agency administrator, went to Gulfport, Mississippi, to talk with disaster victims and inspect recovery efforts.

The visits and meetings will help the presidential commission "begin to lay the groundwork for our efforts going forward, to determine what really to concentrate on and where to put our priorities and, very importantly, what the people most affected by all of this think about how effective the response has been," Reilly said.

President Barack Obama established the bipartisan commission last month and gave members six months to investigate the oil catastrophe in the Gulf of Mexico. The panel will listen to public comments and official testimony from BP, the U.S. Coast Guard and the National Oceanic and Atmospheric Administration on the recovery efforts.

CNN's John King, Kim Segal, Vivian Kuo, John Lisk and Shelby Lin Erdman contributed to this report.