Diesel's street margin is near its widest in a month at 1.384 a gallon

The diesel retail-wholesale spread is 1.384 a gallon right now. The spread is the gap between what you pay at the rack and what you charge at the pump, and it has widened in your favor. If you are moving diesel, the street margin is fatter today than it has been for most of the last month.

Part of that is retail diesel itself, now 5.652 a gallon and at the very top of its 30-day range, which ran from 3.459 to 5.652. Retail has climbed 6.4 percent in a month and pump prices have kept pace, so the spread held instead of getting squeezed. Gasoline went the other way. RBOB is 3.061 a gallon, down 5.0 percent over 30 days and sitting near the bottom of its range at the 30 percent mark. Diesel is where the margin is today; gasoline is soft.

For anyone buying refined product, the refiner side tells a quieter story. The 3:2:1 crack spread is 58.43, down 4.81 over the past month. Refining margins are tighter than they were, which usually means less incentive to push extra barrels through the system. Petroleum inventories are 428.91, up 6.0 percent but only at the 40 percent mark of their range, so supply is comfortable without being heavy.

The crack spread is the one to watch. It has been narrowing while retail diesel holds at the top of its range, and if refiner margins keep tightening, the wholesale cost under your diesel spread could start to firm up and eat into that 1.384. It may not happen this week, but a tighter crack and a rising rack are the two things that would close the gap you are enjoying now.