Although big pipeline projects have attracted a lot of attention in recent years, shipping via rail has remained a popular option for those who move oil, with 10 percent of American crude production in 2014 transported by rail. But given that rail is often more expensive and less reliable than pipelines, why is it still shouldering a sizable portion of the job of moving America’s oil? Research from Chicago Booth’s Thomas R. Covert and Chicago Harris’ Ryan Kellogg suggests flexibility may be a big part of the answer—and that planners in other arenas can learn from how the oil industry balances low, fixed costs with high, more variable prices.