More crude flowed into the sea while the cap was off but U.S. Coast Guard Adm. Thad Allen said the step had to be taken "out of an abundance of caution."
BP said on its Web site the lower marine riser package was removed "as a precautionary measure" to "ensure the safety of operations and allow the unexpected release of liquids to be analyzed."
BP spokesman John Curry said oil and gas was being sent through a pipe to the drill ship Discoverer Enterprise again and collection would run at full capacity "as conditions permit," The New York Times reported.
The Transocean rig leased by BP has been spewing oil since April 20, making it the worst oil spill in U.S. history. Eleven workers died when the rig exploded.
Allen also said two Gulf of Mexico oil recovery workers have died -- one while swimming in a pool and the other while operating a boat. There was no indication either death was a direct result of participation in the cleanup, Allen said.
The National Oceanic and Atmospheric Administration said Wednesday it has reopened about 8,000 square miles for fishing in the gulf because oil had not been spotted in the area, the Times reported.
In Washington, Interior Secretary Ken Salazar explained his decision to reinstate a moratorium on deepwater drilling that will include evidence that would "eliminate any doubt" a moratorium was appropriate and within the department's legal authority. On Tuesday a federal judge in New Orleans issued a temporary injunction on the six-month ban.
Weather forecasters say a tropical wave in the Caribbean could move into the gulf, carrying potentially more bad news for oil cleanup efforts.
AccuWeather.com said Wednesday the strength of the system expected to enter the gulf by early next week is questionable, but there is a risk of squalls and rough seas in oil slick and cleanup-containment operation areas.