The deliveries of the drilling units are expected in the fourth quarter of 2013 and second quarter of 2014, respectively.
The firm added it had entered into all four vessel building contracts with the subsidiaries of Sevan Drilling ASA, a unit of Sevan Marine.
Separately, COSCO said it had made effective a $114 million contract with ATP Oil and Gas to build a topside module -- a production unit for oil and gas -- which is scheduled for delivery in the third quarter of 2013.
COSCO shares were hit last week after news broke that Sevan Marine had cancelled its planned $275 million rights issue and was seeking restructuring as it could not meet its project liquidity and financing requirements.