OSLO, Aug 20 (Reuters) - Offshore drilling rig contractors Transocean Ltd and Dolphin Drilling have made a new offer to buy the assets of stricken rival Seadrill Ltd , Dolphin"s chief executive said on Friday. Oslo-listed Seadrill, founded by Norwegian-born tycoon John Fredriksen, is currently seeking to emerge from U.S. Chapter 11 bankruptcy proceedings under an alternative financial plan filed in court last month. "I can confirm that Dolphin and Transocean submitted an updated bid yesterday," Dolphin Chief Executive Bjoernar Iversen told Reuters. For the bid by the two rivals to succeed, however, they would have to persuade Seadrill"s creditors that their offer is superior to the company"s own plan. (Reporting by Nerijus Adomaitis; Editing by Terje Solsvik and David Clarke) Our Standards: The Thomson Reuters Trust Principles.