The TSS is the internationally recognised shipping lane system through the Strait of Hormuz, administered by the IMO. It separates inbound and outbound tanker traffic and carries roughly 20% of global oil supply. Its legal foundation is a 1968 tripartite agreement between Iran, Oman, and the IMO.Source: IMO

What is the 1968 Hormuz Traffic Separation Scheme?

A tripartite framework agreed between Iran, Oman, and the IMO in 1968, governing lane separation through the Strait of Hormuz for 58 years. IMO Secretary-General Dominguez surfaced it in April 2026 as a legal constraint on both Iran’s IRGC corridor and the Northwood Coalition’s rules of engagement.Source: IMO

What did Iran do to the Hormuz shipping lanes in April 2026?

On 9 April 2026, the IRGC published mine charts overlaying a danger zone over the standard TSS lanes through Hormuz, directing ships to Larak Island IRGC-supervised corridors instead. Zero tankers transited on the Ceasefire’s first day.Source: ISNA / Tasnim / Kpler / Lowdown update 63

Background

A Traffic Separation Scheme (TSS) is an IMO-designated maritime routing system that divides inbound and outbound vessel traffic through congested straits and waterways, functioning like motorway lanes at sea. First codified under Rule 10 of the International Regulations for Preventing Collisions at Sea (COLREGS) and SOLAS V/10, TSS corridors exist in dozens of straits and approaches worldwide. The IMO approves and formally adopts each scheme; compliance is mandatory for vessels of SOLAS signatory states. The Hormuz TSS in particular carries approximately 20% of global oil supply through two designated lanes separated by a buffer zone, making it among the most heavily trafficked and strategically sensitive TSS corridors on earth.

The Hormuz TSS came under direct operational threat in the 2026 Iran conflict. On 9 April 2026, the IRGC published danger zone charts overlaying the standard TSS lanes with a maritime exclusion area, directing vessels toward Larak Island corridors under IRGC escort instead. IMO Secretary-General Arsenio Dominguez responded on 17 April with a formal statement invoking UNCLOS and rejecting any tolls or discriminatory passage measures, surfacing a pre-existing multilateral framework governing the TSS's legal status. The legal question sharpened further when the Northwood Coalition, drafting rules of engagement for the 51-nation Hormuz escort initiative, had to choose whether to operate within or around the IMO framework.

By 20 June 2026, the TSS had effectively been abandoned as the primary transit corridor. The Joint Maritime Information Center (JMIC) issued an advisory warning of possible mines in the standard TSS lanes and clearing a southern alternative: the corridor through Oman's territorial waters, mine-free, with transponders on and no US Navy coordination required. CENTCOM reported 55 merchant vessels carrying 17 million barrels transited via the Omani route on 20 June alone. The episode illustrated how a nominally legal maritime construct can be rendered operationally void through mine threat alone, without any formal annulment of the scheme's IMO status.