Office Depot Inc. is buying smaller rival OfficeMax Inc. in what it’s calling a “merger of equals,” creating a heftier office-supply company to challenge industry leader Staples.

In the $1.2 billion all-stock deal, OfficeMax shareholders will receive 2.69 Office Depot shares for each OfficeMax share, valued at $13.50 each.

Together, the two companies said they expect to better “meet the growing challenges of a rapidly changing industry,” anticipating annual revenue of about $18 billion. Staples had $25 billion in sales in 2011.

“Consumers and business-to-business customers are increasingly demanding a seamless omnichannel experience across retail stores, direct sales, telesales and digital environments,” the companies said in a statement. “By integrating these touchpoints effectively, the combined company expects to build lasting brand loyalty.”

OfficeMax and Office Depot have suffered declining sales since the recession and fight to generate a 3 percent profit margin, compared with a margin of 8 percent or more at Staples, said IBISWorld analyst Dale Schmidt.

“The hope is that the resultant company could cut redundant costs, raising its profit margin, while retaining a market share that will compete with Staples,” he said.