Before the bell:

U.S. stocks were set to extend gains Tuesday, following world markets higher, as investors awaited a confidence vote for Greek Prime Minister George Papandreou.
The vote of confidence, held by the Greek parliament, may determine whether Papandreou's government has the strength to avoid a default and secure a rescue package.
Despite ongoing anti-government protests, investors are largely expecting Papandreou to win the vote, said Mark Luschini, chief investment strategist, Janney Montgomery Scott.
U.S. stocks managed gains Monday, even as investors remained cautious about Greece's debt crisis.
World markets:

Economy: Wall Street will get May existing home sales data from the National Association of Realtors at 14:00 GMT. Economists expect the pace of existing home buying to slow to 4.79 million annualized units, down from 5.05 million units in April.
Companies: Credit union regulators sued JPMorgan (JPM, Fortune 500) and Royal Bank of Scotland (RBS) for selling mortgage bonds that were designed to fail -- leading federal credit unions to lose more than $800 million. Shares of JPMorgan rose 0.8%, while Royal Bank of Scotland's stock edged lower.
Shares of Bed Bath & Beyond (BBBY, Fortune 500) jumped more than 4% after Jefferies reaffirmed its "buy" rating and $62 price target for the company's stock -- expecting Bed Bath & Beyond to beat earnings estimates in the first quarter.
Best Buy Inc. (BBY, Fortune 500)'s board authorized a new $5 billion share repurchase program to replace its previous $5.5 billion share repurchase program. Shares of the company rose 4.3% in premarket trading.
Shares of Renren (RENN) gained 2.5% before the market open, after the Chinese social-networking site reported a narrower loss in the first quarter, as sales increased 47%.
Drugstore chain Walgreens (WAG, Fortune 500) reported third-quarter results before the opening bell that beat expectations, posting record earnings and revenue.
Oil for July delivery gained $1.08 to $94.34 a barrel.
Gold futures for August delivery rose $3.10 to $1,545.10 an ounce.
Bonds: The price on the benchmark 10-year U.S. Treasury edged lower, pushing the yield up to 2.98% from 2.96% late Monday.