A BP spokesman said Friday in an e-mail to The Associated Press that the 50-foot, 300-ton device was detached from the wellhead at 1:20 p.m CDT.
The device was slowly being lifted to the surface and wouldn't likely reach the top until sometime Saturday.
Earlier in the day, a vessel had latched onto the equipment to raise it from a mile beneath the sea.
The blowout preventer is considered a key piece of evidence in the spill investigation.
Investigators will examine it and hope to gain insight into why the device failed to prevent the spill.