US STOCKS-Futures edge lower as oil suffers worst day since May 2011
* Oil falls 6.5 percent, Exxon tumbles in premarket
* Dow on track to turn negative for the week
* Dow down 34 pts, S&P down 4.5 pts, Nasdaq up 7.75 pts
By Ryan Vlastelica
NEW YORK, Nov 28 (Reuters) - U.S. stock index futures were lower on Friday, with energy shares likely to be under heavy pressure in a holiday-shortened session as crude oil tumbled to a four-year low.
* Wall Street was closed for the U.S. Thanksgiving holiday on Thursday and will shut three hours earlier on Friday. Trading volatility could spike since many market participants were extending the holiday.
* U.S. crude futures slumped 6.5 percent to $68.93 per barrel. It was the biggest one-day drop for crude since May 2011, and brought prices to their lowest since 2010. On Thursday, OPEC decided not to cut output, which could leave oil markets heavily oversupplied.
* Energy shares have been under pressure throughout 2014 as crude prices has slid almost 36 percent from a recent closing high. The S&P energy sector is the only S&P 500 industry group to be lower for the year, down 4.3 percent.
* The Energy Select Sector SPDR exchange-traded fund fell 4.7 percent to $81.31 in premarket trading while Dow component Exxon Mobil Corp lost 4.5 percent to $90.20, on track for its biggest one-day drop since August 2011. Chevron Corp fell 4.3 percent to $100.20 while Halliburton Co lost 6 percent to $44.50. Continuación...