Japanese retail group Seven i Holdings plans to expand its web of U.S. convenience stores to 20,000 following the $21 billion deal to buy American counterpart Speedway, it was learned Monday.

The company's 7-Eleven chain is already the biggest in the U.S., with about 9,000 stores. In addition to Speedway's 4,000 or so existing outlets, the group plans to further build the network, distancing itself from Canada's Alimentation Couche-Tard, the No. 2 operator in the U.S., which has around 6,000 including Circle K shops.

The plans were revealed in an earnings conference of U.S. oil refiner Marathon Petroleum, Speedway's current owner.

"We plan to work hand in hand with Seven-Eleven as they grow out their portfolio," Marathon President and CEO Michael Hennigan said. "They have a stated goal to expand to about 20,000 stores."

Hennigan said the two sides have "a second agreement" under which Marathon will continue to supply the network "beyond the existing Speedway situation."

The fusion of online and brick-and-mortar stores is proceeding apace in the U.S., spurred by the spread of the novel coronavirus. With the $21 billion deal, Seven & i accelerates its effort to challenge Amazon.com and other rivals online in one of the world's biggest retail markets.

The deal, the biggest corporate acquisition worldwide since the coronavirus outbreak early this year, also will be Seven & i's biggest such purchase, easily surpassing its $3.1 billion acquisition of Texas-based convenience store chain Sunoco LP in 2018.

Seven & i abandoned its initial bid for Speedway this spring, after it failed to reach an agreement on the price in exclusive negotiations with Marathon. Some of the Japanese retailer's board members said the price tag, said to be about $22 billion, was too big.