West Texas Intermediate crude futures dropped below $100 a barrel for the first time since May 11 as concerns grow that a global economic slowdown will ultimately hobble demand. Traders are worried about the impact of sharply higher US borrowing costs, as the Federal Reserve embarks on a series of interest-rate hikes intended to cool inflation. Adding to bearish sentiment, Citigroup Inc. said that oil prices could collapse to $65 a barrel by the end of this year and slump to $45 by end-2023 if a demand-crippling recession hits.