Stock index futures rose sharply on Monday as global stocks gained after China's vow to allow a flexible yuan exchange rate boosted investor appetite for risky assets.

China's yuan surged the most since its revaluation in 2005 following the surprise weekend announcement by China's central bank that it would allow greater flexibility for the currency.

The move is expected to boost purchasing power and demand in China, the world's third largest economy. A higher yuan would also help temper inflation by pushing down import prices, which could mean Beijing would have less need to tighten monetary policy aggressively.

World stocks hit a five-week high, while the euro and commodities jumped and oil futures rose more than 1 percent to $78.23 a barrel.

S&P 500 futures were up 17.1 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 jumped 141 points, and Nasdaq 100 futures advanced 29.5 points.

Stocks ground higher in another lightly traded session on Friday, ending a nervous week with gains despite signs of economic weakness at home and worries about public debt troubles in Europe.

An internal BP Plc document released by a U.S. lawmaker estimated that a worst-case scenario rate for the Gulf of Mexico oil spill could be about 100,000 barrels per day, far higher than the current U.S. figure. BP's U.S.-listed shares slipped 3.5 percent to $30.66 in premarket trading.

Dell Inc is in talks with Google Inc over the use of the Chrome operating system on its laptops, a top Dell executive said.

(Reporting by Leah Schnurr; editing by Jeffrey Benkoe)