For 10 years prior to 2018, the differential between propane prices at the Conway, KS, hub averaged less than a nickel per gallon below Mont Belvieu. In fact, between 2013 and 2017, the price spread was only 3.5 c/gal — excluding a winter 2014 Polar Vortex aberration — which basically reflects the cost of moving barrels 700 miles north-to-south. Not this year, though. After starting 2018 at 3 c/gal, the propane price spread took off, and has averaged 18 c/gal since April, some days moving above 26 c/gal, far above the per-bbl cost of transporting propane 700 miles south to Mont Belvieu. Is it pipeline capacity constraints? In part. But there is a much more significant factor driving this differential wider, not only in the propane market, but across all five of the NGL purity products. What is this mysterious factor? To find out, read on. But here’s your first clue: the problem is not in Kansas anymore.