Dark

Heavy ReadingThe WCSB supply letter

Sections

Iran watch

Iranian oil exports under sanctions and naval blockade: tanker-tracked export estimates, floating storage, grades and rerouting, the shadow fleet, and China's buying. Every figure carries its vintage.

Read this page as the sanctioned sour barrel: Iran's exports are the largest single pool of distressed medium and heavy sour crude, and every number here is either tracker-observed or claimed, never both. Bullets say which, so treat Iranian state media figures as claims and tanker-tracker figures as observations.

Iran is the marginal sour barrel in Asia: its exports land in the same Chinese teapot refineries that buy the Urals and other grades competing with Western Canadian Select (WCS). When Iranian barrels are blocked, teapots bid up substitute sours and the whole sour complex firms, supporting Canadian differentials; when the blockade loosens and Iranian crude flows again, medium and heavy sours soften first. The floating storage stockpile is the leading indicator: it is supply that can move without a single new barrel being produced.

Updated September 24, 2026 · refreshes weekly

The blockade timeline

• The current war was triggered February 28, 2026 by joint US and Israeli strikes on Iran; Iran responded by closing commercial access to Hormuz. The US blockaded Iranian ports from April 13.
  Reported Sep 2026; accessed 2026-09-24 Hormuz watch (Heavy Reading)
• The US blockade of Iranian ports started April 13, 2026; United Against Nuclear Iran (UANI) measures exports by vessels crossing the blockade line from the eastern point of Oman to the Iran-Pakistan border, exiting the Gulf of Oman, rather than by point of loading.
  Reported ~Jun 2026; accessed 2026-09-24 Seatrade Maritime (citing UANI)
• Mid-June 2026, the Islamabad memorandum of understanding (MOU) took effect and the US lifted the naval blockade under a sanctions waiver; Iran exported roughly 50 million barrels in the following two weeks (~1.66 million b/d in June, per TankerTrackers), and Iran's parliament speaker put the post-blockade figure above 40 million barrels.
  Jul 1, 2026; accessed 2026-09-24 RFE/RL (via GlobalSecurity)
• In the 26 days after the MOU signing, Iran exported more than 80 million barrels of crude and products, worth over $6 billion at prevailing prices, per TankerTrackers.
  Jul 14, 2026; accessed 2026-09-24 WANA (citing TankerTrackers)
• Between the June 14 MOU announcement and July 6, Iran exported roughly 55 million barrels valued above $4.5 billion; pre-war, a typical month was 47-50 million barrels (~$3.05B), so the waiver window generated ~47% more revenue in 22 days than a full pre-war month.
  Jul 8, 2026; accessed 2026-09-24 JINSA (citing TankerTrackers)
• Washington restored the blockade on July 14, 2026; Kpler, Vortexa and TankerTrackers identified no Iranian crude cargo vessel successfully transiting Hormuz to China after that date.
  ~Sep 2, 2026; accessed 2026-09-24 National Security Journal (citing Vortexa, Kpler, Reuters)
• On September 22, 2026, TankerTrackers spotted the first Iranian crude exports in two months: very large crude carriers (VLCCs) Diona (IMO 9569695) and Hero2 (IMO 9362073) plus the Suezmax tanker Sonia I exiting past the blockade line at the east end of the Gulf of Oman; Kpler confirmed four Iran-linked tankers exiting the Gulf of Oman.
  Sep 23, 2026; accessed 2026-09-24 Maritime Executive (citing TankerTrackers, Kpler)

Exports: what the trackers see

• Iran's seaborne oil exports were 587 million barrels in 2024 (+10.75% y/y); China took 533 million barrels, 91% of the total, up 24% from 2023.
  Year-end 2024 review; accessed 2026-09-24 UANI (via Maritime Executive)
• Iran exported 666 million barrels in 2025 (+13.5% y/y), with China by far the largest buyer.
  Year-end 2025 review; accessed 2026-09-24 UANI (via Infomarine / Maritime Executive)
• March 2026 loadings were ~2.0 million b/d; July fell to ~749 kb/d of crude and condensate; August loadings were only ~220-255 kb/d.
  ~Sep 2, 2026; accessed 2026-09-24 National Security Journal (citing Vortexa, Kpler, Reuters)
• May 2026 exports by sea were just 2.01 million barrels vs 29.7 million in April (-93%); the May total was four Panamax/Handymax naphtha shipments to China plus limited liquefied petroleum gas (LPG). Very large crude carrier (VLCC) 2-million-barrel crude shipments dropped to zero.
  May 2026 data; accessed 2026-09-24 Seatrade Maritime (citing UANI Tanker Tracker)
• Iran's pre-war baseline exports were 1.68 million b/d; TankerTrackers estimated they had fallen to zero by early September 2026 and could remain there 'for the foreseeable future' depending on any agreement.
  Sep 6, 2026; accessed 2026-09-24 RFE/RL (citing TankerTrackers)
• Iranian state media claimed August 2026 oil exports above $3 billion, the highest monthly figure in two years, sharply at odds with tracker estimates of ~220-255 kb/d loaded that month; treat as claimed, not tracked.
  Sep 19, 2026; accessed 2026-09-24 StoryChase (citing Iranian state media)

Floating storage

• Iranian floating crude was ~29 million barrels on September 8, 2026, down from ~90 million in mid-July, the blockade drew down pre-war floating stock by roughly two-thirds (Kpler, via WSJ).
  Sep 8, 2026; accessed 2026-09-24 WSJ via Kpler (compiled in Oil Depletion Report)
• Vortexa's broader measure, all Iranian crude stored aboard tankers, fell from ~135 million barrels at end-July to ~107 million by August 26; Iran is drawing down crude that had already cleared the blockade without replacing it.
  ~Sep 2, 2026; accessed 2026-09-24 National Security Journal (citing Vortexa)
• Iran sold about 9 million barrels (~$900M) out of floating storage in the Gulf of Oman, vessels already clear of Iranian ports when enforcement began, hence outside the blockade's reach.
  ~Sep 10, 2026; accessed 2026-09-24 Maritime Executive (citing TankerTrackers)
• TankerTrackers estimated ~30 million barrels of Iranian crude awaiting export in mid-July, with ~60 million barrels of floating storage capacity available in surrounding waters as a buffer if production faced restrictions.
  Jul 14, 2026; accessed 2026-09-24 WANA (citing TankerTrackers)

What grades are stuck, and what unwinds first

• Iran's export stream is medium and heavy sour crude: Iran Light (medium sour, American Petroleum Institute (API) gravity 33.6, 1.46% sulfur) and Iran Heavy (heavy sour, API gravity about 29.5, sulfur about 1.77%), per National Iranian Oil Company (NIOC) assays reported by S&P Global Platts.
  Sep 2023 Hellenic Shipping News (citing S&P Global Platts)
• China's independent refiners buy mainly Iran Light and some Iran Heavy. They crack Iran Light directly in their crude distillation units; Iran Heavy has to be blended with lighter grades first.
  Mar 2024 Hellenic Shipping News
• Iran Light is a direct substitute for Russian Urals in China's teapot refineries (independent refiners): similar medium sour specs (Iran Light 33.6 API and 1.46% sulfur vs Urals 31.7 API and 1.19%), and teapot sources say Iranian barrels suit their units better than Russian ones.
  Sep 2023 Hellenic Shipping News
• Scarcity is already pricing in: Kpler reported Iran Light flipping from a $3.50 per barrel discount to a $3.50 premium over Intercontinental Exchange (ICE) Brent within a week as available floating cargoes thinned.
  Aug 2026 OilPrice.com (citing Kpler)
• Kpler put total Iranian crude outside the Persian Gulf and Gulf of Oman at about 83 million barrels, with about 40 million at Singapore's Eastern Outer Port Limits (EOPL) anchorage, but only about 4 million barrels of that still unsold. An unwind would mostly deliver already-sold cargoes, not flood the spot market.
  Aug 2026 OilPrice.com (citing Kpler)
• The reroute path back is Kharg Island loadings, transit through the Gulf of Oman, ship-to-ship transfer at EOPL Malaysia, delivery to Shandong teapots. Kpler notes teapots have been substituting Russian Urals and fuel oil while Iranian barrels were blocked, with the Eastern Siberia-Pacific Ocean (ESPO) blend sold out weeks in advance.
  Aug 2026 OilPrice.com (citing Kpler)
• So the grades hit hardest by a return are medium and heavy sours: Russian Urals first (direct teapot substitute), then the wider medium-sour complex. Light sweets are less exposed, though record ESPO premiums of $20 to $30 per barrel over Brent would also ease.
  Sep 2026 Reuters via Baird Maritime, Sep 2026

The shadow fleet

• UANI's 'ghost armada' reached 560 tracked tankers at end-2025 after 83 new vessels were identified during the year; of 180 tankers sanctioned in 2025, 108 had been previously identified by UANI.
  Year-end 2025 review; accessed 2026-09-24 UANI (via Infomarine / Maritime Executive)
• TankerTrackers identified two US-sanctioned tankers in ballast that penetrated the blockade inbound for Iran with Automatic Identification System (AIS) transponders on; the US Navy claims 13 Iranian tankers have been turned back so far.
  ~Sep 10, 2026; accessed 2026-09-24 Maritime Executive (citing TankerTrackers)
• During the June waiver window, 30+ tankers carrying 50M+ barrels of Iranian crude headed for Asia (Kpler); UANI separately tracked ~15 large Iranian-registered tankers departing Iranian ports with Automatic Identification System (AIS) transponders switched on, a break from dark-fleet practice. For years, cargoes were masked via ship-to-ship (STS) transfers at Malaysia's Eastern Outer Port Limits (EOPL) before continuing to Asia.
  ~Jun 24, 2026; accessed 2026-09-24 MarineInsight (citing Kpler, UANI)
• Treasury Secretary Bessent said the US sent warning letters to banks in China, Hong Kong, the UAE and Oman over continued Iranian-oil business, threatening secondary sanctions, 'the financial equivalent of a bomb' on Iran's oil sales system.
  ~Sep 10, 2026; accessed 2026-09-24 Maritime Executive (citing TankerTrackers)

China: the buyer of last resort

• China imported ~431 million barrels of Iranian oil in 2023 (over 80% of Iran's exports), rising to ~533 million in 2024 (over 91%), largely via ghost-fleet tankers offloading through intermediaries before reaching China.
  Testimony Apr 1, 2025; accessed 2026-09-24 Claire Jungman, UANI (House Foreign Affairs testimony)
• Treasury Secretary Bessent said June 29, 2026 that despite the US lifting sanctions on Iranian oil, no country except China had bought at a discount, others held back fearing sanctions snapback.
  Jul 1, 2026; accessed 2026-09-24 RFE/RL (via GlobalSecurity)
• China is expected to remain the biggest buyer via independent refiners; UANI's Charlie Brown noted it was unclear whether exporters would abandon the established EOPL ship-to-ship transfer networks even under the waiver.
  ~Jun 24, 2026; accessed 2026-09-24 MarineInsight (citing UANI)

Where sources disagree

• Iranian floating storage: Kpler (via Wall Street Journal, Sep 8, 2026) vs Vortexa (via National Security Journal, ~Sep 2, 2026). Kpler put Iranian floating crude at about 29 million barrels on September 8, down from about 90 million in mid-July, while Vortexa's broader measure, all Iranian crude stored aboard tankers, was about 107 million barrels on August 26. Different scopes and different dates: the two measures are not directly comparable, a definitional difference rather than a data conflict.

For the WCSB book, watch the floating storage drawdown and the blockade line: they tell you how much Iranian sour is coming before any official announcement. A sustained return of Iranian barrels would pressure the medium and heavy sour grades that price off Urals first, and Canadian heavies would feel it at the margin. The Iran Light premium flipping from discount to premium shows how fast the sour complex reprices when barrels vanish.

Standing watch

What the daily feed updates on this page.

• Monthly UANI Tanker Tracker export totals and ghost-armada additions
• TankerTrackers / Kpler / Vortexa export-loading and floating-storage snapshots
• US blockade enforcement actions (US Central Command (CENTCOM), Joint Maritime Information Center (JMIC), UK Maritime Trade Operations (UKMTO) advisories)
• US Treasury Office of Foreign Assets Control (OFAC) shadow-fleet sanctions designations
• China-bound flows and EOPL ship-to-ship transfer activity
• International Energy Agency (IEA) Oil Market Report monthly Iran production estimates
• Iranian grade differentials to ICE Brent (Iran Light premium/discount as a scarcity gauge)

Gaps

• Kpler and Vortexa publish different floating-storage scopes (Kpler ~29M bbl of floating crude Sep 8 vs Vortexa ~107M bbl of crude aboard tankers Aug 26); the two are not directly comparable, definitional difference, not a data conflict.
• Iranian state media claimed August 2026 exports above $3B, a two-year high, while Vortexa/Kpler tracked only ~220-255 kb/d loaded that month, claimed vs tracked, unresolved.
• The exact count of sanctioned vessels laden vs in ballast changes daily; no public source publishes it continuously.

Sources