U.S. stock index futures pointed to a lower open on Friday after Chevron Corp warned about its second-quarter earnings, raising the specter of a weaker-than-expected second-half economic recovery and anemic corporate profits.

* After the bell Thursday, Chevron said second-quarter earnings would be hit by a sharp decline in U.S. refining margins and that any benefits from higher oil prices would be largely offset by a weaker dollar.

* Alcoa Inc posted a better-than-expected loss Wednesday, adding a positive tone to the start of earnings season. Stocks are likely to be pushed and pulled as major companies release financial scorecards and investors focus on the corporate outlook for the rest of the year.

* Economic data on tap includes the preliminary reading for July's Reuters/University of Michigan survey of consumer sentiment, due at 9:55 a.m. EDT. The data is expected to come in at 70.5, down from 70.8 in June, according to the average forecast of economists polled by Reuters.

* S&P 500 futures fell 6.30 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures lost 64 points, and Nasdaq 100 futures gave up 9.50 points.

* In the auto sector, General Motors Corp prepared to exit bankruptcy, saying it was a leaner and meaner automaker ready to win back American consumers and pay back taxpayers after its 40-day reorganization.

* On Thursday, stocks edged higher as investors bought beaten-down technology and commodity shares and a positive broker comment on Goldman Sachs Group Inc boosted the financial sector.

(Reporting by Leah Schnurr; editing by Jeffrey Benkoe)

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