Normally there will be 6-7 points diff between spy and es at the beginning when an es future becomes main stream contract, then the diff will become smaller and smaller, I think the diff will be near zero when the es future is expired. But now, the es (dec / 2014) is near due, but the diff between spy and es (dec/ 2014) is still almost 5-6 points， what is wrong? will this 5-6 points disappear in these 2 weeks? I have a short-es contract in hand, does this mean I will pay 5-6 point as holding cost if I hold the es contract for 2 weeks until it expires?
SPY goes ex dividend 12/19 so it currently reflects a pending dividend payout, thus the premium vs SPX. If you do nothing with your ES it will financially settle against the SPX opening range on 12/19. Of course you could roll the ES_Z to ES_H during futures rollover day next Thursday.