Goldman: 90-day diesel export ban could cut wholesale diesel by up to 25 cents a gallon a week until storage fills

A 90-day ban on US diesel exports, if Washington orders one, could hand fuel retailers a short window of fatter forecourt margins before it turns against them. Goldman Sachs figures a suspension would push diesel prices lower at first, by about $0.25 a gallon each week, and keep pushing until domestic storage fills up. For a c-store operator, falling wholesale cost that the street price lags is exactly where diesel margin comes from.

The margin window

Retail fuel margin is the gap between what you pay the rack and what you charge at the pump, and it widens when wholesale drops faster than you cut the sign. Goldman's math points to wholesale diesel coming down while there's tank space to soak up the barrels that would have gone overseas. Operators who don't chase the street price down day for day could see diesel margin run wide for a few weeks.

That window has a hard edge. The relief only lasts while storage has room.

When the tanks fill

Once domestic diesel storage fills, the mechanics flip. Barrels that can't be exported and can't be stored have nowhere to go, and Goldman warns pump prices climb from there. The bank's read is that gasoline prices head higher as the system backs up. For a forecourt, that means the early diesel-margin cushion gives way to rising costs on both grades, and street prices that have to move up to keep pace.

The timing depends on how fast tanks reach the top, which the reports don't pin down. A 90-day ban could spend its first stretch cheap and its back half expensive.

What it means inside the store

Fuel is the draw; the margin is inside. Cheaper diesel for a few weeks may pull more trucks and more traffic onto the lot, which is foodservice and packaged sales you wouldn't otherwise ring up. If the second half of a ban lifts pump prices, the risk runs the other way, with higher fuel cost trimming the discretionary spend that loyalty programs and hot food lean on.

None of this is ordered yet. It rests on reports that Washington may suspend diesel exports for 90 days, and Goldman's estimate of what would follow.

What to watch

Whether the administration actually moves on a diesel export suspension, and for how long. How quickly domestic diesel storage tightens once exports stop, since that's the switch between the cheap phase and the expensive one. And whether gasoline follows diesel higher on Goldman's read, or holds while the diesel barrels back up first.