(Adds share price) 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 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. Seadrill"s Oslo-listed shares traded 5.5% up by 1425 GMT, after jumping about 30% earlier on Friday. Norwegian business daily Finansavisen, which was first to report the new offer, said the bid valued Seadrill"s assets at $1.7 billion. Iversen declined to comment on details of the new proposal. For the bid by the two rivals to succeed, they would have to persuade Seadrill"s creditors that their offer is superior to the company"s own restructuring plan. Seadrill said it remained focused on its plan. "This has the support of almost two-thirds of our creditors, who not only support our plan but (also) our long-term business strategy and plans to emerge, with expediency, from Chapter 11," Seadrill spokesperson Iain Cracknell said. Reuters reported in July that a consortium comprising Transocean, Dolphin Drilling and an unidentified party, had lodged a competing bid for Seadrill earlier in the month. Offshore driller Noble Corp , which itself came out of bankruptcy in February, submitted a bid for Seadrill"s assets in May, a court filing showed. Dolphin is owned by Strategic Value Partners (SVP), a firm focused on distressed debt and private equity with $17.5 billion in assets under management and is one of Seadrill"s creditors. Seadrill is seeking to restructure more than $7 billion of debt in exchange for handing control of the company to its creditors. The company operates 43 drilling rigs, including 10 managed on behalf of other firms. Transocean was not immediately available for comment. (Reporting by Nerijus Adomaitis; Editing by Terje Solsvik, David Clarke and Barbara lewis) Our Standards: The Thomson Reuters Trust Principles.