US STOCKS-Energy leads Wall St lower; S&P set for 3rd down week
* S&P poised for third straight weekly decline
* FXCM jumps on results, Aeropostale down on outlook
* Dow down 0.4 pct, S&P down 0.2 pct, Nasdaq up 0.1 pct (Updates to market open)
By Ryan Vlastelica
NEW YORK, March 13 (Reuters) - U.S. stocks mostly fell on Friday, putting the S&P 500 on track for its third straight weekly decline as the dollar strengthened while continued weakness in crude oil prices pressured energy shares.
Markets have been volatile this week, with the S&P posting both its biggest one-day gain since early February and its biggest one-day loss since early January.
Crude oil fell 2.1 percent after the International Energy Agency said a global oil glut was building and U.S. oil production showed no signs of slowing. The commodity has fallen in six of the past seven sessions.
The S&P energy index fell 1 percent, among the biggest decliners of the 10 primary S&P 500 sectors. Chevron Corp fell 1.4 percent to $101.03 while Occidental Petroleum lost 1.4 percent to $73.50.
"It's a bit of a surprise that the U.S. continues to produce at such a high level, and that amount of oil surplus continues to push the commodity lower," said Michael Arone, chief investment strategist for State Street Global Advisors' U.S. Intermediary Business in Boston. Continuación...