Tumbling oil prices and a stronger dollar are pushing down U.S. corporate profits for the first time in more than five years, hurting companies from Exxon Mobil Corp. to Wal-Mart Stores Inc. First-quarter earnings per share for companies in the Standard & Poor's 500 Index may have fallen about 5.8 percent, according to estimates compiled by Bloomberg, in the first year-over-year decline since 2009's third quarter. As earnings season gets its unofficial start this week with Alcoa Inc., the biggest drag will come from a 63 percent profit decline at energy companies.