SemGroup’s Board of Directors may redeem the rights for $0.001 per right at any time before an event that causes the rights to become exercisable. Under the Plan’s terms, the Rights will expire on the date one day after the date of SemGroup’s 2012 Annual Meeting of Stockholders.In addition to the adoption of the Rights Plan, the SemGroup Board of Directors has unanimously adopted amendments to the Company’s bylaws (the “Bylaw Amendments”) relating to the setting of a record date and other procedures applicable to shareholder action by written consent. Details regarding the Rights Plan and the Bylaw Amendments will be contained in a Form 8-K to be filed by SemGroup with the U.S. Securities and Exchange Commission. SemGroup stockholders will receive information regarding the Rights Plans shortly. Barclays Capital and LCT Capital are serving as SemGroup’s financial advisors and Wachtell, Lipton, Rosen & Katz is serving as legal counsel to SemGroup and its board of directors. About SemGroup Based in Tulsa, OK, SemGroup® Corporation (NYSE: SEMG) is a publicly traded midstream service company providing the energy industry the means to move products from the wellhead to the wholesale marketplace. SemGroup provides diversified services for end-users and consumers of crude oil, natural gas, natural gas liquids, refined products and asphalt. Services include purchasing, selling, processing, transporting, terminalling and storing energy. SemGroup® is a registered trademark of SemGroup Corporation. ADDITIONAL INFORMATION This communication does not constitute an offer to buy or solicitation of an offer to sell any securities or a solicitation of any vote, consent or approval. No tender offer for the shares of SemGroup has commenced at this time. If a tender offer is commenced, SemGroup may file a solicitation/recommendation statement with the U.S. Securities and Exchange Commission (“SEC”). Any solicitation/recommendation statement filed by SemGroup that is required to be mailed to stockholders will be mailed to stockholders of SemGroup. In addition, SemGroup may file a proxy statement and other documents with the SEC. Any definitive proxy statement will be mailed to stockholders of SemGroup. INVESTORS AND SECURITY HOLDERS OF SEMGROUP ARE URGED TO READ THESE AND OTHER DOCUMENTS FILED WITH THE SEC CAREFULLY IN THEIR ENTIRETY IF AND WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION. Investors and security holders will be able to obtain free copies of these documents (if and when available) and other documents filed with the SEC by SemGroup through the web site maintained by the SEC at http://www.sec.gov. A registration statement relating to the common units of the Master Limited Partnership has been filed with the Securities and Exchange Commission, but has not yet become effective. These securities may not be sold nor may offers to buy be accepted prior to the time the registration statement becomes effective. This announcement does not constitute an offer to sell, or the solicitation of an offer to buy, any securities. Any offers, solicitations of offers to buy or sales of securities will only be made in accordance with the registration requirements of the Securities Act of 1933 or an exemption therefrom.