U.S. oil prices tumbled Monday to their lowest level in 18 months as plunging stock prices on Wall Street added to fears of a global economic slowdown that could reduce oil demand just as crude production and supplies are surging higher. •Light, sweet crude for February delivery ended 6.7% lower at $42.53 a barrel on the New York Mercantile Exchange in a trading session that ended about an hour early due to Christmas Eve. The closing price was the lowest since June 21, 2017. …