* Futures off: Dow 39 pts, S&P 5 pts, Nasdaq 9 pts
By Rodrigo Campos
NEW YORK, Jan 5 (Reuters) - U.S. stock index futures fell on Monday as volume returned to markets after the New Year holiday, with energy shares sliding again as crude prices fell to fresh 5-1/2 year lows.
* Commodities are likely to be pressured further by the strength in the U.S. dollar. A measure of the greenback against a basket of major currencies hit its highest since December 2005.
* Crude oil futures prices dropped to their lowest since May 2009 amid a global supply glut and lackluster demand. Russia's oil output hit a post-Soviet high last year, and Iraq's oil exports were at the highest since 1980 in December.
* An exchange-traded fund that tracks the performance of S&P 500 energy stocks was down 1.4 percent in premarket trading.
* Shares of Cempra Inc jumped near 30 percent after it moved closer to approval of its lead antibiotic, solithromycin, after an oral version of the potential blockbuster met the main goal in a late-stage trial.
Futures snapshot at 7:21 a.m. EST (1221 GMT):
* S&P 500 e-minis were down 5 points, or 0.24 percent, with 141,995 contracts changing hands.
* Nasdaq 100 e-minis were down 9 points, or 0.21 percent, in volume of 25,195 contracts.
* Dow e-minis were down 39 points, or 0.22 percent, with 23,479 contracts changing hands. (Editing by Bernadette Baum)