Public anger over high gasoline prices is turning to a familiar target - Wall Street. The role of speculative investors in this year's price spike has come under increasing scrutiny in recent weeks, nowhere more so than in Washington. Nearly 70 members of Congress wrote a stern letter Monday to a federal commission that regulates the country's main market for crude oil, demanding that the commission crack down on speculation. President Obama, his energy policies under attack from Republicans, ordered a fresh look at speculation's role in the market on Tuesday. This is just another example, in my view, of Wall Street playing the casino," said Rep. Jackie Speier, D-Hillsborough, who signed the letter to the Commodity Futures Trading Commission. "Everyone should be outraged that every time they're filling up their tank, they're paying a premium because of speculation." How big is that premium? One of the trading commission's five members estimated last month that speculative investors were adding 56 cents to the price of each gallon of gas. As a result, Honda Civic drivers pay an additional $7.39 per fill-up, said Commissioner Bart Chilton. Owners of the Ford F150 pickup pay an extra $14.56. Speculative investors include hedge funds and investment banks that buy contracts for the future delivery of oil but never intend to take possession of the fuel itself. They buy and sell strictly as a financial investment, and their presence in the market has swelled.