Future and Cash index prices are always different until contract expiry. Future prices include the cost of carry, dividend payment and hence may trade at a premium (often in the case of WTI Crude contracts) or discount (as often in the case for stock indices). The discount/premium will get closer to the underlying cash prices as expiry nears. We are currently trading March 2012 stock index contracts and hence there is a significant discount when you look at cash index vs stock index future.