When do US sanctions on Iran move a share price?

Hengli Petrochemical, 2026: Dalian refinery sanctioned

Short answer: the warning was the trend, not anything naming Hengli. The detailed reporting came after.

The action: on 2026-04-24 the US sanctioned Hengli Petrochemical (Dalian) Refinery. Treasury called it “one of Iran’s largest customers” for crude oil and said it had bought “billions of dollars’ worth” of Iranian petroleum (Treasury release).
The company’s response: Hengli said in an exchange filing that it had never traded with Iran (Reuters, 2026-04-26, cited in Wikipedia).

The trend: from March to October 2025 the US sanctioned four Chinese oil terminals for taking Iranian oil. They were part-owned by listed companies such as Wintime Energy, Qingdao Port, PetroChina and Sinopec Kantons (our ledger).
Naming Hengli: we found no public report before 2026-04-24. We did not search Hengli’s own Shanghai filings before the action.
After the action: Treasury warned about Chinese independent refineries on 2026-04-28 (Treasury release). The Wall Street Journal published an investigation of Hengli on 2026-08-16.

Before the action (against the local index): −10.0% over 60 trading days, +6.0% over 20, −0.2% over 5.
After: −10.1% after 1 trading day, −4.5% after 5, −25.0% after 20. The first-day fall was the −10% daily limit on the Shanghai exchange.

The shares fell 10% against the index in the three months before, then recovered in the last month. We did not find news that explains the earlier fall.

Share price against the local index, 60 trading days before to 20 after

Share move: the company’s share price change minus the local index change, from daily closing prices (Yahoo Finance).
Before: from the close 60, 20 and 5 trading days before the action, up to the last close before it.
After: from that last close to 1, 5 and 20 trading days later.
Data and code: case_study_summary.csv, case_study_price_paths.csv, scripts/case_studies.py.
Saved sources: receipts/case-studies.