¥3,650/ton — the measured I–III base oil spread today, up ¥820 from September’s average. Three drivers converge: First, two Group I hydrotreating units in East China entered 12-day scheduled maintenance on Oct 4, cutting 125 ktpm capacity — 19% of national Group I output. Second, import window is open: Singapore HVI 150N CFR China main port at $1,095/ton converts to ¥7,342/ton (USD/CNY 6.7050), a 99% premium over domestic Group I ex-works ¥3,692/ton but flat vs. domestic Group III ¥7,342/ton — import substitution is now operationally viable. Third, fuel oil +0.36% and asphalt −3.50% on same day confirm refiners are diverting vacuum residue to coking/asphalt, not base oil cuts — cracking divergence intensifies, squeezing Group I feedstock supply. For SNSUC’s transshipment clients, bonded Group III base oil warehouse receipts now trade at only ¥180/ton premium (vs. ¥420 last month), and blockchain-enabled PCF tags can be embedded into CIF terms — effective price-lock window extended to T+7. Risks are clear: if Brent falls below $98, maintenance may be cut short, collapsing spread below ¥2,900; if Urals arrivals exceed expectations in mid-Oct, Group I feedstock cost declines will also compress spread. We remain long the base oil spread structure. Reversal triggers: Group I operating rate rebounds to 75%, or Group III import arrivals rise >15% w/w.