Oil prices fell for the fourth day in a row on Thursday on fears that high prices have slowed down economic growth in the United States and on burgeoning crude oil stocks. U.S. light crude dropped 98 cents to $50.63 a barrel. London's Brent crude fell 64 cents to $51.65 a barrel. The U.S. economy grew at its softest pace in two years during the first quarter of this year, slowing to a 3.1 percent annual rate of expansion as consumers and businesses curbed spending in the face of rising prices, the U.S. Commerce Department said on Thursday. The growth was below Wall Street expectations for 3.6 percent. A slowdown in economic growth would cap U.S. oil demand growth, which has been a key factor in record high oil prices over the past year.