Suncor Energy Inc. (SU) launched an all-stock hostile bid for Canadian Oil Sands Ltd. valued at about C$4.3 billion ($3.29 billion), as the company increases its focus on Canada's oil sands.

Each Canadian Oil Sands shareholder will receive 0.25 of Suncor shares for each share held, the company said on Oct. 5.

The offer works out to C$8.84 per share based on Suncor's close on Oct. 2 and represents a premium of about 43% to Canadian Oil Sands' last close on the Toronto Stock Exchange.

The deal is valued at about C$6.6 billion including Canadian Oil Sands' debt of C$2.3 billion as of June 30.

Canadian Oil Sands and Suncor are among stakeholders in Canada's largest synthetic crude project, Syncrude, in northern Alberta.

Alberta's oil sands are the world's third-largest crude reserves after Saudi Arabia and Venezuela and a leading source of U.S. crude imports.

Suncor in September bought a tenth of the Fort Hills oil sands project in northern Alberta from French oil company Total SA (TOT).

The tender offer for Canadian Oil Sands will be open until Dec. 4 unless extended or withdrawn, the company said.

Suncor's financial adviser is JP Morgan Securities LLC while Blake, Cassels & Graydon LLP and Sullivan & Cromwell LLP are its legal advisers. ($1 = 1.3076 Canadian dollars)