HOUSTON (Dow Jones)--Testing of a new containment system on a leaking BP PLC (BP, BP.LN) well could continue indefinitely, raising the possibility that no more oil will gush into the U.S. Gulf of Mexico until the Deepwater Horizon spill is permanently killed by a relief well in mid-August, a company official said Sunday. The test, originally scheduled to last 48 hours, has cut off the flow of oil since Thursday, and was extended on Saturday to allow for additional monitoring of the sea floor for signs of new leaks. But BP Chief Operating Officer Doug Suttles said in a teleconference that results so far have been encouraging, with pressure continuing to build up slowly-- a sign that the oil is not escaping the shut-in Macondo well. Both BP and U.S. government scientists are closely monitoring the test. "We're hopeful that if the encouraging signs continue we'll be able to continue the integrity test all the way to the point we get the well killed," said Suttles. "Right now there is no target set to open the well back up to flow." Suttles added that reopening the well remains a possibility if problems are encountered, but so far there have been no issues. "We're just taking this day by day," he said. The first of two relief wells being drilled to permanently kill the leaking Macondo well by flooding it with cement could reach its target by late July, Suttles said. But the kill operation, which involves flooding the leaking well with cement, could last until mid-August, he added. BP will conduct a "ranging run" to determine the location of the first relief well, and will insert the last string of casing into the well, an operation that may take a week to complete, Suttles said. Then the company will resume drilling to finally intersect the Macondo well, a very slow process scheduled to begin in the last week of July. "All things are looking good at this point," Suttles said. BP still has to drill 100 feet vertically and four feet horizontally to reach its target, Suttles added. The capped well was estimated to be gushing between 35,000 and 60,000 barrels of oil a day into the Gulf, beginning shortly after the April 20 blast aboard Transocean Ltd.'s (RIG) Deepwater Horizon rig, which BP had leased to drill a well in its Macondo prospect. The spill, now one of the largest in U.S. history, has had a severe impact on fishing and tourism along the Gulf Coast. BP has paid more than $200 million in damage claims to residents and businesses, and has set up a $20 billion fund to pay for damages related to the spill. Suttles said that as of Sunday morning, the well's pressure was at 6,778 pounds per square inch, and rising at a rate of 1 or 2 psi per hour. The pressure reading, which has climbed more slowly than expected, is a sign that the reservoir is partially depleted. Suttles reported the presence of bubbles in the area being monitored. He said that BP does not believe the bubbles are related to hydrocarbons, but they're being closely watched, he said. -By Angel Gonzalez, Dow Jones Newswires; angel.gonzalez@dowjones.com; 281-536-3064 (Brian Baskin contributed to this article.) (END) Dow Jones Newswires July 18, 2010 09:47 ET (13:47 GMT)