The 21-Mile Width and 10-Mile Traffic Separation Scheme: How the Strait of Hormuz's Physical Constraints Dictate Global Oil Transit

Iran views the 21-nautical-mile-wide Strait of Hormuz as sovereign territorial waters subject to its direct naval routing, while international shipping coalitions treat the passage as a protected transit corridor governed by the 1968 International Maritime Organization (IMO) separation scheme. The physical reality of the strait—a narrow geographic bottleneck handling roughly 20 million barrels of oil per day—forces these two incompatible legal frameworks into direct physical contact.[1][2]

The geography of the chokepoint dictates the mechanics of global oil transit. At its narrowest point between Oman and Iran, the strait spans just 21 nautical miles. However, the navigable channel deep enough for fully laden Very Large Crude Carriers (VLCCs) is significantly narrower. To manage collisions in this constrained space, the IMO established a Traffic Separation Scheme (TSS) that allocates a 10-mile-wide corridor: two 2-mile-wide shipping lanes separated by a 2-mile buffer zone, flanked by safety margins.[1][6]

Under the UN Convention on the Law of the Sea (UNCLOS), the IMO scheme operates on the principle of transit passage, allowing continuous and expeditious transit for all vessels, regardless of flag or cargo. This framework has historically allowed an average of 130 ships to transit the strait daily, carrying 20 to 25 percent of the world's seaborne oil trade and nearly 20 percent of global liquefied natural gas (LNG) exports from Qatar and the United Arab Emirates.[1][2]

Following the escalation of regional conflict in early 2026, the Islamic Revolutionary Guard Corps (IRGC) Navy introduced a competing sovereign transit scheme. Asserting territorial control, Iranian authorities issued formal notices requiring vessels to coordinate directly with the IRGC Navy for approved routing. This ad hoc system effectively bypasses the IMO's 10-mile TSS, directing traffic through alternative lanes closer to the Iranian coast or forcing vessels to navigate newly declared exclusion zones.[4][5]

The IRGC's routing guidance explicitly warns of anti-ship mines in the traditional main traffic zone of the strait, compelling compliance from shipping operators who must balance international legal principles against immediate physical risks. According to Lloyd's List Intelligence, "Vessels transiting the chokepoint must coordinate with the IRGC Navy," fundamentally altering the risk calculus for maritime insurers. By vetting all traffic based on geopolitical affiliation, the sovereign routing framework transforms a neutral geographic bottleneck into a geopolitical toll booth.[3][4]

The physical constraints of the strait leave global markets with few viable alternatives when the 10-mile TSS is compromised. While Saudi Arabia and the UAE maintain pipeline networks designed to bypass the chokepoint, their combined spare capacity is strictly limited by engineering realities.[3][6]

The UAE's Abu Dhabi Crude Oil Pipeline (ADCOP) runs 400 kilometers to the port of Fujairah on the Gulf of Oman, bypassing the strait entirely. It possesses a nameplate capacity of 1.5 million barrels per day, with current utilization leaving room for approximately 700,000 barrels per day of additional emergency volume.[6]

Similarly, Saudi Arabia's East-West Pipeline (Petroline) connects production facilities in Abqaiq to the Red Sea port of Yanbu. While the system has a design capacity of 5 million barrels per day, and Aramco has tested expansions up to 7 million, sustainable flows at maximum capacity remain unproven over long durations. Current estimates suggest between 3 and 5 million barrels per day of spare capacity.[6]

Combined, these overland routes can collectively offset an estimated 3.5 to 5.5 million barrels per day. This leaves a structural shortfall of approximately 15 million barrels per day that cannot be rerouted overland. The sheer volume of crude oil and LNG that must physically pass through the 21-mile gap means that any management framework exercises outsized leverage over the global economy.[2][6]

The tension between these two frameworks is not merely legal; it is operational. Fleet managers must now choose between adhering to the internationally recognized TSS, which may expose vessels to interception or mine risks in contested waters, or complying with the IRGC's routing, which implicitly recognizes Iranian territorial claims and subjects operators to potential tolls and geopolitical vetting.[1][4]

The physical dimensions of the Strait of Hormuz ensure that this localized navigational dispute dictates the baseline cost of global energy. The structural reality is that the strait cannot be bypassed; it must be navigated.[3][6]