SAN FRANCISCO (AP) — Amazon.com Inc. on Thursday reported a surprise loss in the second quarter, as higher revenue was not enough to make up for rising operating expenses. The world's largest online retailer has been spending heavily on order fulfillment and digital content rights, which continue to weigh on profit margins. Amazon has long focused on spending the money it makes to grow its business and expand into new areas from movie streaming to e-readers and even grocery delivery.