They said if there's a quick rise in pressure, they'd open the well immediately to prevent leaks deep underground.
Ever since the cap was put in place last week, engineers have been keeping a close eye on it with underwater cameras and monitoring pressure readings.
BP and the government are still trying to understand why pressure readings from the well are lower than expected. Allen offered two possible explanations: The reservoir the oil is gushing from is dwindling, or there is an undiscovered leak somewhere down in the well.
Officials also said that seepage detected along the sea floor about two miles away does not appear to be related to the ruptured well.
Retired Coast Guard Adm. Thad Allen said BP could keep the cap closed at least another 24 hours, as long as the company remained alert for leaks.
- Work on a permanent plug is moving steadily, with crews drilling into the side of the ruptured well from deep underground. By next week, they could start blasting in mud and cement to block off the well for good. Killing the well deep underground works more reliably than bottling it up with a cap.
- Approximately 94 million to 184 million gallons have gushed into the Gulf over the past three months in one of America's worst environmental crises.
- BP PLC said the cost of dealing with the spill has now reached approximately $4 billion. The company said it has made payments totaling $207 million to settle claims for damages. Almost 116,000 claims have been submitted and more than 67,500 payments have been made.
- Beachgoers have reported less oil fouling the shore since the cap was closed Thursday, saying that conditions have vastly improved from about a month ago.
The Associated Press contributed to this story.