* Brent crude prices, which have fallen 20 percent this year, were down nearly 5 percent as the market braced for oil from Iran to flood an already oversupplied market. * A small recovery in oil on Thursday sent U.S. stocks rallying and helped the S&P 500 to its biggest daily gain since Dec. 4 and send it past the key 1,900 level. * Investors are bracing for weak earnings reports with companies hit by plunging oil prices, concerns over China’s economy and a global economic slowdown.