What a crack spread is
A crack spread is a working proxy for the gross margin that a refinery captures when it turns crude oil into refined products. It is called a crack spread because the refining process breaks, or “cracks,” long crude hydrocarbon molecules into the shorter molecules that make up gasoline, diesel, and jet fuel. The spread is quoted per barrel and expressed in dollars.
The most commonly cited version, and the one on this chart, is the 3-2-1 crack. The name describes a stylised barrel ratio: for every three barrels of crude a refinery processes, roughly two barrels of gasoline and one barrel of distillate emerge from the primary product slate. In the US market the gasoline leg is priced against RBOB (reformulated blendstock for oxygenate blending) and the distillate leg is priced against ULSD (ultra-low-sulfur diesel), the successor to the heating oil contract, both traded on NYMEX. Crude is priced against WTI. The 3-2-1 crack is the value of two RBOB barrels plus one ULSD barrel, divided by three, minus the WTI barrel that produced them.
Other cracks exist for other regions and slates. The Gulf Coast 3-2-1, the Northwest European gasoil crack, and the Singapore crack are the most quoted internationally. Refiners with more complex configurations run their own internal crack proxies that reflect their specific product yields, but the 3-2-1 is the one the futures market watches.
Why the crack spread matters
Refineries operate a discretionary throughput decision every day: how many barrels of crude to run through the primary distillation column. That decision is anchored on the expected margin between crude in and product out. When the crack spread is wide, refineries have strong incentive to maximize throughput, which pulls barrels of crude off the market and pushes barrels of product onto the market. When the crack is thin, marginal refineries can and do reduce runs, particularly when a turnaround (planned maintenance) can be advanced to save on utilisation losses.
The 3-2-1 crack is therefore both a rear-view mirror on refinery profitability and a forward-looking pressure on product availability. A wide crack in the summer driving season is not surprising, but a wide crack that stays wide into shoulder season signals demand strength or product supply tightness that outlives the seasonal pattern.
Why the crack is not the same as refinery earnings
Two important caveats travel with any crack spread reading. First, the 3-2-1 crack captures only the gross value of primary products against front-month crude. It does not net out variable operating costs (natural gas for process heat, hydrogen, catalyst), fixed maintenance, or the value of secondary products that vary refinery to refinery. Refinery reported earnings track the crack directionally but not one-for-one.
Second, the crack uses front-month crude as the input reference, while an actual refinery is running crude that was purchased weeks earlier at prices that may have differed. In fast-moving markets, the reported crack can diverge from the crack that any specific refinery is actually realising.
Seasonal pattern
Product demand has a strong seasonal shape. Gasoline demand peaks with US summer driving. Distillate demand peaks with US and European winter heating. The 3-2-1 crack aggregates both and is generally wider in warmer months, when gasoline pulls the composite up, and softer in shoulder season, when both product legs are between seasonal peaks. The chart draws a five-year seasonal band so the current year can be compared to the recent range and central tendency without any implicit prediction.
What the chart shows and does not show
The chart plots the 3-2-1 crack computed from NYMEX RBOB, ULSD, and WTI front-month futures. The current-year line runs against a five-year band (minimum, average, maximum) so the reader can see whether the current print is within the recent envelope, at the top of it, or below it.
What the chart does not do: it does not translate spread level into refinery earnings, and it does not tell the reader whether the crack is going to widen or narrow next week. The seasonal band is descriptive of history, not a forecast.