Suncor extended its bid for Canadian Oil Sands on Friday, suggesting it fell short of the two-thirds required to win the bid and fueling speculation about how many votes it has received in support of the offer.

In a statement on Monday, Suncor said that it was encouraged by the number of tendered shares but did not specify how many of the votes were supportive of the bid.

Canadian Oil Sands, in a press release, said Suncor is obligated to disclose the tender results.

Suncor is offering Canadian Oil Sands shareholders 0.25 of a Suncor share for each COS share they hold, valuing the target company at C$4.03 billion ($2.84 billion).

The extension of the bid indicates that Suncor is confident that it can swing the rest of the votes in its favor. It is not clear, though, if it can do so without increasing the bid.

Suncor bid for Canadian Oil Sands in October and later extended the bid until Jan. 8.

Syncrude in northern Alberta is Canada's largest single source of crude oil, and Canadian Oil Sands has a 36.7 percent stake in the asset.

Canadian Oil Sands shares were up 0.5 percent at C$7.51 on Monday, while Suncor shares slipped 1.2 percent to C$32.84.

(Reporting by John Tilak; Editing by Chizu Nomiyama and Meredith Mazzilli)

By John Tilak

Stocks treated in this article : Canadian Oil Sands Ltd, Suncor Energy Inc.