The offer price of 26.50 Norwegian crowns per share represents a 98.5 percent premium over Friday's close of 13.35 crowns for the Norwegian company, which was spun off from Aker Solutions earlier this year.

Aker Drilling operates two harsh environment, ultra-deepwater semi-submersible rigs and is expected to take delivery in 2013 of two drillships under construction.

"The transaction is also expected to be immediately accretive to Transocean's earnings," Transocean said in a statement.

Aker Drilling's main owner Aker Capital AS on Sunday agreed to sell its 41 percent stake in the company, and Transocean has also received irrevocable pre-commitments of 19.5 percent of the outstanding shares from other shareholders, including funds managed by TPG-Axon Capital.

Copyright Reuters, 2011