On 21 October, front-month fuel oil stood at 4,747/t CNY (-1.02%) and bitumen at 4,472/t CNY (-0.82%). Both fell, but the ordering reversed: fuel oil moved back above bitumen by 275/t CNY. At the start of the month this spread was -579/t CNY (bitumen the pricier one), flipping positive in under three weeks.

The flip changes internal refinery feed routing. With fuel oil dearer than bitumen, delayed-coker units prefer to keep resid for bunker blending or road bitumen rather than run it as coker feed - higher feed cost suppresses the marginal output of petroleum coke and paraffin. Conversely, when bitumen is relatively cheap, some heavy ends divert to coking, easing coke supply.

For SNSUC's thirteen-category base, petroleum coke and paraffin do not sit on the live quote screen but are derived products at the tail of the heavy-oil chain. Every swing in the fuel oil/bitumen spread first hits coker feed economics, then shows up in those two items' inventory and pricing. Operators watching the board should treat the FO-BIT spread as a leading indicator for the coking chain, not just track the two crude benchmarks.

The current +275/t CNY gap is still narrow; the coker-switch threshold typically sits around plus or minus 400/t CNY. Below that, units will not reshuffle feed at scale, so coke and paraffin quotes stay range-bound near term, but traders should pre-secure some forward coke positions against a supply squeeze if the spread punches through the threshold.