U.S. diesel is $5.454 a gallon, near the top of its month

Diesel retail is $5.454, up 6.2 percent over the past 30 days and at 91 percent of its 30-day range. The low over that window was $3.459, so the street price is almost as high as it has been all month. For anyone hauling or reselling, your cost to refill the rack is close to its ceiling right now.

The margin side helps a little. The retail-wholesale spread is $1.017 a gallon, up 0.002 over 30 days, so the gap between what you pay wholesale and what you charge at the pump is a hair wider than a month ago. It is not much, but on high-priced product a penny of spread holds up better than it does when diesel is cheap. ULSD futures back this up, at $4.174 and 77 percent of their own range, so the wholesale side is firm too and not about to hand you relief.

Gasoline is the other direction. RBOB is $2.941, down 6.6 percent over 30 days and sitting at just 18 percent of its range, close to the month's floor of $2.756. If you sell both fuels, the split is stark right now: diesel high and firm, gasoline soft and near its lows. The 3:2:1 crack is $58.48, down 0.79 over 30 days, so refiner margins tightened a touch but are still healthy.

Watch the diesel wholesale line into next week. With retail near the top of its range and futures firm at $4.174, street diesel could hold here or push higher if the wholesale number keeps climbing, and your refill cost may not ease. Gasoline looks set to stay cheap by comparison unless RBOB lifts off its floor.