Exactly the same product. Exactly the same day. In storage very nearby. Yet their prices diverged by 17 cents per gallon — a spread equivalent to $7 per barrel. That’s a very substantial difference for prices that typically are almost indistinguishable, differing by an average of only 0.3% in recent years. The disparity roiled the financial underpinnings of exports for over a month and busted numerous inventory hedges. Is this some rare commodity? Hardly. It’s Mont Belvieu propane, the Rock of Gibraltar benchmark propane price in the U.S., and to a great extent around the world. But during October there was a crack in that rock a mile wide.