Why does ethylene tar pricing track crude oil so closely?

Why does ethylene tar pricing track crude oil so closely?
Ethylene tar sits at the bottom of a chain running crude to ethylene to pyrolysis tar to coumarone resin to anode coating material. Because it is a byproduct of naphtha cracking, its price moves broadly in step with crude, and that pass-through has squeezed coating-material margins since 2020 as both tar and resin prices climbed. Yet the link is not mechanical. In mid-2022 tar and resin prices diverged from crude, and downstream buyers have learned to treat the correlation as a guide rather than a rule. Annual tar output grows steadily at roughly one-tenth of ethylene volume, so supply is fairly predictable while demand from coatings and carbon black swings with margins.