Norwegian offshore driller Seadrill Ltd has entered into an agreement to buy Aquadrill LLC in an all-stock deal that values the British firm at $958 million, the companies said on Friday. As part of the deal, the unitholders of the UK-based offshore driller Aquadrill will receive about 30.65 million shares of Seadrill, which represents a 38% ownership in the company, they said in a joint statement.