Staples has a market value of about $11 billion, while Office Depot has a market value of about $4.1 billion. A merger would help fend off intense competition from online retailers such as Amazon.com Inc and big-box chains such as Wal-Mart Stores Inc that sell the same core office supplies, such as paper and ink toner, for less. Office Depot and Staples were not immediately available for comment outside regular U.S. business hours.