Oil prices fell more than 4 percent to below $50 a barrel on Monday, pressured partly by expectations the world economy could suffer another blow if a flu outbreak in Mexico turns out to be the start of a pandemic. U.S. crude oil futures for June delivery were down $2.49 at $49.06 a barrel by 1033 GMT, erasing some of Friday's gains of $1.93 that brought the contract to settle at $51.55. London Brent crude was down $2.33 at $49.34 a barrel. The flu outbreak in Mexico has killed more than 100 people and already spread to the United States, prompting fears of a pandemic that boosted the U.S. dollar and hit equity markets in Asia and Europe. (For more stories on the flu outbreak, click.) Gains in the dollar, a safe-haven in times of stress, also helped depress oil, which tends to fall when the U.S. currency rises. Airline shares were hit by expectations the flu outbreak could affect air travel, which could also reduce demand for jet fuel. "Nervousness about another batch of US earnings reports and macro reports, coupled with a potential pandemic out of Mexico, are both weighing on prices," said Edward Meir of broker MF Global in a research note. "The Mexican situation is resurrecting fears of the chilling impact that the SARS epidemic had on economic growth." TACTICAL SHORTS Oil is down about $100 a barrel from a record peak in July last year of more than $147. The global recession and shrinking oil demand had pushed prices toward $30 a barrel earlier this year. They have recovered to around $50 alongside an equity market rally. "Commodity prices and returns have risen substantially since mid-February lows," Goldman Sachs said in a research note. "We believe markets will likely continue to pullback from current levels in the near term, as fundamentals are not yet stable enough to support higher prices," the bank said. "As a result, we have opened tactical shorts in both the oil and metals markets in recent days."

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