* EPL Oil to be acquired by Energy XXI for $2.3 bln
* Express slumps after outlook
* Copper drops to lowest level in nearly four years
* Futures down: Dow 42 pts, S&P 5.5 pts, Nasdaq 13 pts
By Chuck Mikolajczak
NEW YORK, March 12 (Reuters) - U.S. stock index futures fell on Wednesday, putting the S&P 500 on track for a third day of declines, as concerns grew over the strength of China's economy.
* London copper, seen as a proxy for China's economic health, fell to its lowest level since July 2010. Recent economic data has shown signs of economic slowing, while with the country's first ever bond default last week has increased concerns that financing deals that use the industrial metal as collateral could unravel.
* Geopolitical issues continued to be monitored by investors as earnings season has drawn to a close and amid a light economic calendar this week.
* Ukraine's government appealed for Western help on Tuesday to stop Moscow annexing Crimea but the Black Sea peninsula, overrun by Russian troops, seemed fixed on a course that could formalize rule from Moscow within days.
* S&P 500 e-mini futures fell 5.5 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 42 points and Nasdaq 100 futures declined 13 points.
* EPL Oil & Gas Inc jumped 41.4 percent to $38.25 in light premarket trading after the company agreed to be acquired by larger rival Energy XXI Ltd for $2.3 billion, including debt.
* Express Inc dropped 12.6 percent in premarket trading after the apparel retailer reported fourth-quarter earnings and forecast a profit for the current quarter that fell far short of analyst expectations.
* Oxigene Inc surged 145 percent to $5.93 before the opening bell after the company said its experimental drug Zybrestat combined with Roche's cancer drug Avastin significantly slowed progression of recurrent ovarian cancer better than Avastin alone in a midstage clinical trial.
* European shares fell, weighed down by below-forecast earnings reports and fears of more corporate defaults in China as a persistent decline in the copper price hit the mining sector.
* Asian stocks fell as economic uncertainty in China and the United States combined with political tensions in Ukraine to keep investors cautious.