OSLO (Reuters) - Seadrill , the world's biggest offshore driller by market capitalisation, won a two-year $497 million (296.21 million pounds) contract from ExxonMobil (>> Exxon Mobil Corporation) for one of its newly built rigs, the firm said on Friday.

The deal, which also includes a one-year option, is for work in Nigeria, in support of the ERHA North Phase 2 project, the firm said.

The rig, under construction by Samsung Heavy Industries (>> Samsung Heavy Industries Co.,Ltd), will be delivered in September.

(Reporting by Balazs Koranyi, editing by Terje Solsvik)