S&P index futures added to gains on Wednesday following the release of August durable goods data.

S&P 500 futures rose 7.8 points and were above fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration of the contract. Dow Jones industrial average futures gained 43 points, and Nasdaq 100 futures added 6.5 points.

Futures were already in positive territory, indicating stocks will climb for a fourth straight session as investors remained encouraged by progress toward plans to ease the euro zone's debt woes.

(Reporting by Ryan Vlastelica; editing by Jeffrey Benkoe)