U.S. stock index futures rose on Monday as investors welcomed details of a fiscal aid package for Greece and focused on a merger that would create the world's largest airline.

European countries agreed to a 110 billion-euro ($146.5 billion) aid package for debt-laden Greece, the biggest ever financial bailout of a country.

The lack of specifics on the deal weighed on U.S. markets in recent weeks, and the agreement offered relief to investors. But European stocks fell on concerns that the package may face political obstacles and on doubts that Greece can implement the tough austerity measures it has promised in exchange.

UAL Corp , parent of United Airlines, said it will buy Continental Airlines Inc for $3.2 billion in stock, a deal that would form the world's largest airline.

The Greece package is providing a relief to the market, although the relief may be temporary. We are starting off today with an early bounce from an oversold situation on Friday, said Peter Cardillo, chief market economist at Avalon Partners in New York.

S&P 500 futures were up 4.9 points and 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 rose 33 points, while Nasdaq 100 futures were up 10.25 points.

Warren Buffett on Sunday intensified his feisty defense of a controversial mortgage transaction marketed by Goldman Sachs Group Inc , saying the investment bank's behavior does not warrant public fury. Buffett also said he is seeing signs of improvement in the economy, especially in manufacturing, though he said it will take another year for a sustainable housing recovery to take hold.

Goldman Sachs shares rose 1.8 percent in premarket trade to $147.74.

Due at 8:30 a.m. Monday are March figures for personal spending and income, and at 10 a.m. ET, March construction spending data and ISM manufacturing data for April.

The median Reuters forecast of 32 economists for the ISM's manufacturing index is 60.0, up from 59.6 in March. Construction spending is forecast to have fallen 0.3 percent month over month in March, according to a Reuters poll.

The market will also keep a close eye on car sales for April. Ford Motor Co rose 1.9 percent to $13.27 in premarket trade ahead of its April sales report expected to show a double-digit increase over the same period a year ago.

Energy shares will be in the spotlight again as the huge oil slick caused by an underwater leak continued to creep toward the U.S. Gulf Coast on Monday. The Obama administration pressed energy giant BP Plc to stem the oil gushing from its ruptured offshore well. U.S.-traded shares of BP fell about 2.8 percent in premarket trade to $50.67.

China on Sunday raised the proportion of deposits that lenders must keep in reserve at the central bank, another step in the country's campaign to remove excess cash in the economy.

U.S. stocks tumbled on Friday to close out the worst week since January as news of a criminal probe into Goldman Sachs unnerved investors already anxious about the prospects for heavy regulation from Washington. But the three major U.S. stock indexes have racked up gains for the last three months.

(Editing by Padraic Cassidy)