Filed by: Suncor Energy Inc.

Pursuant to Rule 425 under the Securities Act of 1933, as amended

Subject Company: Canadian Oil Sands Limited

Form F-80 File No.: 333-207268

[The link provided in the advertisements above connects to a web site including the advisories reproduced below.]

The information on and accessible through this website and videos and advertisements prepared by Suncor Energy Inc. (“Suncor”) that have linked you to this website (collectively, the “Information”) relates to an exchange offer (the “Offer”) commenced by Suncor for all the outstanding shares of Canadian Oil Sands Limited (“COS”). Please read the important notices below.

NOTICE TO U.S. HOLDERS

The Offer is being made for the securities of a Canadian issuer by a Canadian issuer that is permitted, under a multijurisdictional disclosure system adopted by the United States, to prepare the Offer documents in accordance with the disclosure requirements of Canada. COS Shareholders in the United States should be aware that such requirements are different from those of the United States. The financial statements included or incorporated by reference in the Offer documents have been prepared in accordance with International Financial Reporting Standards, and are subject to Canadian auditing and auditor independence standards, and thus may not be comparable to financial statements of U.S. companies.

COS Shareholders in the United States should be aware that the disposition of their shares in COS (“Shares”) and the acquisition of Suncor common shares by them as described in the Offer documents may have tax consequences both in the United States and in Canada. Such consequences for COS shareholders who are resident in, or citizens of, the United States may not be described fully in the Offer documents.

The enforcement by COS shareholders of civil liabilities under U.S. federal securities laws may be affected adversely by the fact that each of Suncor and COS are incorporated under the laws of Canada, that some or all of their respective officers and directors may be residents of a foreign country, that some or all of the experts named in the Offer documents may be residents of a foreign country and that all or a substantial portion of the assets of Suncor and COS and said persons may be located outside the United States.

THE SUNCOR COMMON SHARES OFFERED AS CONSIDERATION IN THE OFFER DOCUMENTS HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE UNITED STATES SECURITIES AND EXCHANGE COMMISSION (“SEC”) OR ANY U.S. STATE SECURITIES COMMISSION NOR HAS THE SEC OR ANY U.S. STATE SECURITIES COMMISSION PASSED UPON THE ACCURACY OR ADEQUACY OF THE OFFER DOCUMENTS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

COS Shareholders should be aware that, during the period of the Offer, Suncor or its affiliates, directly or indirectly, may bid for or make purchases of Suncor common shares or Shares, or certain related securities, as permitted by applicable law or regulations of the United States, Canada or its provinces or territories.

Suncor has filed a registration statement on Form F-80, as it may be amended from time to time, which includes the Offer documents, with the SEC in respect of the Offer. The Information is not a substitute for such registration statement or any other documents that Suncor has filed or may file with the SEC or send to shareholders in connection with the Offer. INVESTORS AND SHAREHOLDERS ARE URGED TO READ THE REGISTRATION STATEMENT ON FORM F-80 AND ALL OTHER RELEVANT DOCUMENTS FILED OR TO BE FILED WITH THE SEC IN CONNECTION WITH THE OFFER AS THEY BECOME AVAILABLE, AS WELL AS ANY AMENDMENTS OR SUPPLEMENTS TO THOSE DOCUMENTS, BECAUSE THEY CONTAIN OR WILL CONTAIN IMPORTANT INFORMATION. You will be able to obtain a free copy of the registration statement on Form F-80, as well as other filings containing information about Suncor, at the SEC’s website (www.sec.gov).

NOT AN OFFER

Except as provided in the next sentence, the Information does not constitute an offer to buy or sell, or an invitation or a solicitation of an offer to buy or sell any securities of COS or Suncor. The Offer is made exclusively by means of, and subject to the terms and conditions set out in, the Offer and Circular, dated October 5, 2015, as amended from time to time, and the related Letter of Transmittal and Notice of Guaranteed Delivery. While the Offer will be made to all holders of COS shares, the Offer will not be made or directed to, nor will deposits of shares be accepted from or on behalf of, holders of shares in any jurisdiction in which the making or acceptance of the Offer would not be in compliance with the laws of such jurisdiction. However, Suncor may, in its sole discretion, take such action as it may deem necessary to extend the Offer to holders of COS shares in any such jurisdiction.

Forward-Looking Statements

The Information contains certain “forward-looking statements” within the meaning of the United States Private Securities Litigation Reform Act of 1995 and “forward-looking information” within the meaning of applicable Canadian securities legislation (collectively, “forward-looking statements”), including statements about the Offer including statements about the Offer (including the proposed transaction summary (consideration, premiums, key metrics, pro forma ownership and key conditions and timing) and the expected COS shareholder potential benefits and expected pro forma benefits); Suncor’s expected future growth projects; synergies, savings, and commitments to the Syncrude project; Suncor’s anticipated future production growth; reserve life for each entity; capital expenditures; the NYMEX CL Light Sweet Crude Oil Futures contract settlement prices; and expectations with respect to dividends, share repurchases and future oil exposure, which are based on Suncor’s current expectations, estimates, projections and assumptions that were made by Suncor in light of its experience and its perception of historical trends. Some of the forward-looking statements may be identified by words such as “estimates”, “plans”, “goal”, “strategy”, “expects”, “continue”, “may”, “will”, “outlook”, and similar expressions. In addition, all other statements and other information that address the Offer (including satisfaction of the Offer conditions, those relating to the tax treatment of shareholders, the expected timing of the consummation of the Offer, and certain strategic and financial benefits

and operational and cost efficiencies expected to result from the consummation of the Offer) are forward-looking statements. Forward-looking statements are not guarantees of future performance and involve a number of risks and uncertainties, some that are similar to other oil and gas companies and some that are unique to Suncor. Users of this information are cautioned that actual results may differ materially as a result of, among other things, assumptions regarding expected synergies and reduced operating expenditures; volatility of and assumptions regarding oil and gas prices; assumptions regarding timing of commissioning and start-up of capital projects; fluctuations in currency and interest rates; product supply and demand; market competition; risks inherent in marketing operations (including credit risks); imprecision of production and reserves estimates and estimates of recoverable quantities of oil, natural gas and liquids from Suncor’s properties; the ability to access external sources of debt and equity capital; the timing and the costs of well and pipeline construction; assumptions regarding the timely receipt of regulatory and other approvals; the ability to secure adequate product transportation; changes in royalty, tax, environmental and other laws or regulations or the interpretations of such laws or regulations; applicable political and economic conditions; the risk of war, hostilities, civil insurrection, political instability and terrorist threats; assumptions regarding OPEC production quotas; and risks associated with existing and potential future lawsuits and regulatory actions.

Although Suncor believes that the expectations represented by such forward-looking statements are reasonable, there can be no assurance that such expectations will prove to be correct. Suncor’s management’s discussion and analysis (“MD&A”) for the period ended September 30, 2015 (the “Third Quarter MD&A”) and dated October 28, 2015, 2014 Annual Report and its most recently filed Annual Information Form/Form 40-F and other documents it files from time to time with securities regulatory authorities describe the risks, uncertainties, material assumptions and other factors that could influence actual results and such factors are incorporated herein by reference. Copies of these documents are available without charge from Suncor at 150 6th Avenue S.W., Calgary, Alberta T2P 3E3, by calling 1-800-558-9071, or by email request to info@suncor.com or by referring to the company’s profile on SEDAR at www.sedar.com or EDGAR at www.sec.gov. Except as required by applicable securities laws, Suncor disclaims any intention or obligation to publicly update or revise any forward-looking statements, whether as a result of new information, future events or otherwise. Suncor’s actual results may differ materially from those expressed or implied by its forward looking statements, so readers are cautioned not to place undue reliance on them.

The financial and operating performance of Suncor and its reportable operating segments and the timing and terms upon which the Offer may be consummated, if at all, may be affected by a number of factors. Many of these risk factors and other assumptions related to Suncor’s forward-looking statements and information are discussed in further detail throughout the Offer Documents, the Third Quarter MD&A, and in Suncor’s 2014 annual MD&A, 2014 Annual Information Form and Form 40-F on file with Canadian securities commissions at www.sedar.com and the United States Securities and Exchange Commission at www.sec.gov, and readers should refer to such risk factors and other statements in evaluating the forward-looking statements contained on this website.