Alimentation Couche-Tard Inc (ATDb.TO) and Japan's Seven & i Holdings Co Ltd have submitted indicative offers to acquire U.S. convenience store retailer CST Brands Inc (CST.N), people familiar with the matter said on Thursday.

The strong interest in CST underscores the wave of consolidation sweeping the North American convenience store sector, as retailers try to cope with low profit margins and find savings through gaining scale.

Couche-Tard and Seven & i, the owner of U.S. convenience store chain 7-Eleven, are competing against several other bidders for CST, including a consortium of private equity firms Blackstone Group LP (BX.N) and Apollo Global Management LLC (APO.N), the people said.

CST will seek at least one more round of offers before deciding if will sell itself, the people cautioned. The sources asked not to be named because details of the sale process are confidential.

A Seven & i spokesman denied it made an offer, saying it was not interested in buying the entire company although 7-Eleven earlier this year bought 76 CST stores in California and three stores in Wyoming for US$408 million.

CST and Blackstone declined to comment, while Couche-Tard and Apollo did not immediately respond to requests for comment.

CST shares rose over 18 per cent to US$44.95 on the news, giving the company a market capitalization of around US$3.4 billion.

CST, spun off from Valero Energy Corp (VLO.N) in 2013, is one of the largest publicly traded fuel retailers in North America. 

Based in San Antonio, Texas, CST owns and operates convenience stores and gas stations in Canada and the U.S. It also controls the general partner of gas station company CrossAmerica Partners LP (CAPL.N).

CST has been working with investment banks JP Morgan Chase & Co (JPM.N) and Bank of America Corp (BAC.N) to explore a sale after coming under pressure from activist investors JCP Investment Management and Engine Capital LP.

A sale of CST would follow similar deals in the sector. In 2014, Marathon Petroleum Corp's (MPC.N) subsidiary Speedway acquired oil and gas company Hess Corp's (HES.N) retail operations and other assets for US$2.82 billion.

Last March, Couche-Tard closed its acquisition of The Pantry, a Cary, North Carolina-based convenience store chain, in a deal valued at US$1.7 billion, including debt.