OSLO (Bloomberg) — Seadrill ASA, the Norwegian oil-rig company set up by billionaire John Fredriksen, bid 3.77 billion kroner ($684 million) for Aker Drilling ASA, trumping a rival offer by Aker Capital.

Seadrill said it will offer 40.5 kroner a piece for Aker Drilling, in a statement to the Oslo Stock Exchange. That's eight percent more than the closing price of Aker Drilling on December 12, the day before Aker Capital said it raised its stake to above 40 percent, triggering a mandatory offer under Norwegian law.

Aker Drilling jumped 4.9 percent to close at a record 43 kroner in Oslo, valuing the company at four billion kroner.

The Seadrill offer is 4.4 percent above the 38.78 kroner a share that Aker Capital, an investment company based in Norway and controlled by billionaire Kjell Inge Roekke, paid for its 45 percent stake in Aker Drilling. Seadrill is the second-largest shareholder in Aker Drilling with a 25 percent stake.

"I think the Seadrill bid will go through," said Anders Hagen, an analyst with ABG Sundal Collier in Oslo.

"This shows Seadrill wants to grow further in the deepwater drilling market," said Hagen, who has a "hold" rating on Aker Drilling shares and a "buy" for Seadrill.

Rental rates for offshore rigs have soared as oil companies such as Exxon Mobil vie for scarce supplies of equipment used to drill wells amid surging energy prices. Given the long waits at shipyards, it's quicker to get hold of rigs by buying a company than by ordering them, analysts say.

Aker Drilling has two semi-submersible rigs under construction that are scheduled to be delivered in April and October 2008.

Demand is especially strong for semi-submersible rigs and drillships that operate in deep waters as companies drill wells in areas that are harder to reach to replenish their dwindling reserves.

Seadrill, run from Norway and based in Hamilton, Bermuda, said the offer will be made in cash and is subject to the company getting more than 90 percent of Aker Drilling shares. The world's sixth-largest offshore driller has made several acquisitions, including a $2.4 billion purchase of rig owner Smedvig ASA.