Global oil prices dipped below $90 a barrel for the first time in more than two years Thursday as investors saw new signs that global supplies will continue to surpass demand. Both Brent, the global benchmark, and the U.S. standard are trading more than 20% below a recent high, meeting the definition of a bear market. Prices have slumped for nearly four months as global supplies remain ample. At the start of PIRA Energy Group’s widely attended seminar in New York on Thursday, the research firm predicted oil prices have further to fall, Reuters reported. PIRA is typically considered optimistic on energy prices, market participants say. The seminar is closed to the press.