OAK BROOK, Ill. (AP) -- McDonald's says its same-store sales climbed 5.1% in May, as the hamburger chain continued to prosper from budget-conscious consumers. The Oak Brook, Ill.-based company says U.S. same-store sales climbed 2.8 percent, helped by classic menu items and its new McCafe espresso-based coffees. European same-store sales surged 7.6 percent, while same-store sales for Asia Pacific, the Middle East and Africa rose 6.4 percent. Same-store sales, or sales at stores open at least a year, are a key indicator of retailer performance because they measure growth at existing stores rather than newly opened ones.