Marathon Petroleum Corp.'s Speedway LLC , Alimentation Couche-Tard Inc. and Energy Transfer Partners LP's Sunoco Inc. are among those interested in a potential acquisition of activist-pressured convenience store operator CST Brands Inc., reports The Deal's Sarah Pringle, citing a source familiar with the situation. Besides an outright sale of CST Brands to one of the large consolidators, the odds of a proxy fight are also high, the unnamed source said, noting that the window to nominate directors opens in early March. Arnaud Ajdler's Engine Capital LP on Wednesday delivered a letter to the board of CST Brands requesting that it either take various actions to substantially improve business operations or launch a review of strategic alternatives, including the exploration of a sale. In addition to Engine Capital, with an approximately 1% stake in CST Brands, the company's shareholder base includes Alan Fournier's Summit, N.J.-based hedge fund Pennant Capital Management LLC and Daniel Lewis' Orange Capital LLC, which own about 4.6% and 3.1% of the company, respectively. CST Brands, based in San Antonio, is amongst North America's largest publicly traded fuel and convenience store retailers and encompasses more than 1,900 retail locations in the U.S. and Canada under banners that include Corner Store, Depanneur du Coin and Nice N Easy.