Staples is considering selling itself, and is in talks with private-equity bidders, a source familiar with the matter said on Tuesday, sending the largest U.S. office supplies retailer's shares up about 15 percent. The stock was last up 11 percent.

The retailer last year called off a proposed merger with rival Office Depot due to antitrust concerns.

Both companies have since announced cost-cutting plans and sold most of their European operations to focus on their North America businesses.

Framingham, Massachusetts-based Staples had a market value of $5.65 billion as of Monday.

Staples has reported falling sales for the last five years as it faces growing competition from Amazon.com and other online sellers, as well as big-box retailers such as Costco Wholesale and Wal-Mart Stores.

Staples spokesman Mark Cautela declined to comment.

Office Depot's shares rose about 5.3 percent to $4.94 in morning trade.

The Wall Street Journal reported earlier that Staples was exploring a sale.