Early last year, Citi's New York-based global head of commodity research, Ed Morse, made a bold claim: the world was entering an era of cheap oil. "[The] $90 per barrel (/bbl) floor on the world oil price over the past few years will become a $90/bbl ceiling," he said in an interview with Barron's, published in March 2014. An average of $75/bbl was conceivable in the years to come, he added.

It seemed unlikely. The previous day, front-month West Texas Intermediate (WTI) crude oil futures traded