By James Herron Of DOW JONES NEWSWIRES LONDON (Dow Jones)--The amount BP PLC (BP) has spent on the Gulf of Mexico oil spill rose to $3.95 billion Monday, and the company said tests on a well cap that has halted the flow of oil for several days continue to behave as expected. The pressure in the capped well is 6,792 pounds per square inch and continues to rise slowly, BP said. Rising pressure at the well head should indicate that there are no hydrocarbon leaks from other locations on the well bore. The top U.S. government official overseeing the oil spill response effort asked BP late Sunday to closely monitor hydrocarbons seeping from the sea bed some distance from the Macondo well to ensure that the well bore has not ruptured. The government asked BP to have in place a plan to reopen the well cap as quickly as possible in case the well bore is shown to be damaged. BP said it should have two vessels, the Q4000 and the Helix Producer, in place to capture between 28,000 and 33,000 barrels a day of oil from the well if the cap has to be reopened. "Plans continue for additional containment capacity and flexibility that are expected to ultimately increase recoverable oil volumes to 60,000-80,000 barrels a day," BP said. BP shares have risen by more than a third from their low point on June 29 as the company has made progress containing the spill. The shares closed Friday at 407 pence. -By James Herron, Dow Jones Newswires; +44 (0)20 7842 9317; james.herron@dowjones.com (END) Dow Jones Newswires July 19, 2010 02:32 ET (06:32 GMT)