US STOCKS-Futures edge higher after two-day rally
* Blackberry posts quarterly results
* Brent edges above $60 a barrel
* Futures up: Dow 48 pts, S&P 5.25 pts, Nasdaq 16.75 pts
By Chuck Mikolajczak
NEW YORK, Dec 19 (Reuters) - U.S. stock index futures edged higher on Friday, putting the S&P 500 on track to extend gains after the benchmark index scored its best two-day run in three years.
* The S&P has climbed 4.5 percent over the past two sessions, spurred by the U.S. Federal Reserve's commitment on Wednesday to take a "patient" approach toward raising interest rates while signaling it was on track to raise rates in 2015. That provided clarity and relief to investors over the policy outlook, analysts said.
* Brent crude oil rose above $60 a barrel on Friday, recovering from near a 5-1/2-year low while WTI crude advanced 1.7 percent to $55.02.
* Stocks may experience volatility on Friday as a result of "quadruple witching," the expiration of stock options, index options, index futures and single-stock futures.
* U.S.-listed shares of Blackberry were halted, and were last up 2.8 percent to $10.35 in premarket after the company posted quarterly results. Continuación...