Stock index futures rose on Wednesday, putting Wall Street on track for a third day of gains as optimism grew that Greece's parliament would pass an austerity plan critical to avoiding a debt default.

The vote is expected over the next few hours, and anticipation of parliament's approval has sparked a two-session rally, helping to chop losses partly brought on by the crisis. But gains have come on anemic trading volume, suggesting that caution remained.

In a boost to passage of the austerity measures, one of three rebels in Prime Minister George Papandreou's ruling Socialist party changed heart and said he would support the plan, which is vital to getting bailout funds from the European Union and International Monetary Fund.

U.S. crude oil advanced again, rising 1.2 percent on optimism over the Greece vote. Energy, a weak sector recently, has helped lead stocks higher this week.

S&P 500 futures added 8.3 points and were above 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 gained 58 points, and Nasdaq 100 futures rose 13.5 points.

May pending home sales are scheduled for release at 10 a.m. EDT <1400 GMT> and are seen rising 3.8 percent after a steep fall in the previous month. Positive housing data on Tuesday lifted optimism over the hobbled sector.

Companies scheduled to report quarterly results include Monsanto Co , General Mills Inc and Family Dollar Stores Inc .

Dow component Hewlett-Packard Co plans to develop cloud computing products in China, Chief Executive Leo Apotheker said.

Morgan Stanley's interest rates trading group lost at least tens of millions of dollars betting on inflation expectations in the second quarter, Bloomberg reported, citing sources.

U.S. stocks rose Tuesday, fueled by Greece optimism. The S&P is up more than 2 percent so far this week.

(Editing by Jeffrey Benkoe)