The sharp increase in shares brought Amazon's market value to $247.77 billion, more than its biggest rival, Walmart Stores (WMT), signaling a sea change in retailing. Amazon, which just turned 20, is now valued higher than the world's largest retailer. Bentonville, Arkansas-based Walmart Stores is valued at about $230.53 billion. The company, with 11,767 stores worldwide, still has much higher sales, $485.65 billion in the year ended Jan. 31, compared with Amazon's $89 billion in annual revenue last year. But investors applauded Amazon's ability to keep costs in check while growing its revenue. Amazon credited the profit to continued strength of its cloud-computing business and strong revenue growth both domestically and abroad. That came as it held costs for marketing and package delivery in check.