Transocean Ltd. said it intends to retire four rigs and place them in hold for sale and is looking to identify additional rigs to retire as the company considers the long-term competitiveness of its fleet.

In a June 14 Form 8-K filing, Transocean said it will retire and hold for sale the ultra-deepwater floaters Deepwater Discovery, Deepwater Frontier, and Deepwater Millennium and the midwater floater Songa Trym.

The company made the decision to retire the rigs on June 8 and, as a result, it expects second-quarter earnings results to include an estimated non-cash charge of approximately $520 million.