BP has started pumping cement into the top of its damaged oil well in the Gulf of Mexico as part of its so-called 'static kill' procedure.
Almost three quarters of the oil that leaked from the well has been cleaned up or broken down by natural forces.
The BBC reports cement is complementary to an operation in which the bottom will be sealed with mud and cement.
Work on a relief well is also continuing.
The well ruptured after an explosion and fire on the Deepwater Explorer drilling rig on 20 April, killing 11 workers. The leak was finally stopped on 15 July.
Last week, BP reported a record loss of $US17 billion. It has set aside $US32 billion to cover the costs of the disaster.