British Petroleum (BP) plans to test its new cap on its well for stopping the Gulf oil spill completely, according to Reuters on Wednesday.

The tests are expected to last from six hours to two days. The new cap, which has a better seal than the previous one, was placed on the well on Tuesday.

The only way to completely stop the oil spill is by using the drilling of relief wells to intercept the broken one. The first of these wells started two month ago and is expected to complete by this month, and the final phase will end in August.

"Either through a potential shut-in of the well or being able to produce most if not all of the flow that is generated, either way, we will have a way to contain the oil," U.S. Coast Guard Admiral Thad Allen said.

BP said Monday the cost of cleaning up the oil spill has climbed to 3.5 billion U.S. dollars.