Ethylene crackers have been pricing feedstock far more granularly over the past two years. Naphtha is no longer the default; whenever LPG or ethane land cheaper relative to naphtha, units shift toward the lighter end. That shift peels off a slice of downstream uptake from the heavy grades.

The immediate casualty is the fuel-oil and bitumen side of the heavy barrel. Feedstock light-ending means part of the heavy end no longer runs into the cracker as feed the old way; refiners either sell it out or push it back into coking or the bunker pool, rewriting the regional heavy balance. Today fuel oil rose 3.04% and bitumen 0.87%, on the surface a restock, underneath a symptom of narrowing outlets for the heavy end.

For the seven-grade resale book, light-ending depresses the Asian premium on naphtha-linked cargoes while leaving structural buyers for heavy sour grades. Which origins lean light and which lean heavy moves the landed ranking every quarter. A buying desk cannot treat last year's differential table as this year's guide.

Operationally, watching the light-hydrocarbon landed ratio and the pace of cracker feed switches predicts the next tilt of the heavy chain better than crude up or down alone. Light in, heavy out, is the thread on the unit side this cycle.