Exxon Mobil (XOM) and Chevron (CVX), the nation's two largest integrated oil and gas companies, reported mixed fourth-quarter earnings before the market opened. Exxon, world's largest oil company, said earnings per share rose 12% vs. the same quarter last year to $2.20, topping Wall Street estimates by 20 cents. Edward Jones said in a client note that the better-than-expected profit was due largely to stronger downstream earnings, the business