What is the KOSPI?: The KOSPI (Korea Composite Stock Price Index) is South Korea’s main benchmark stock market index, listing all common shares on the Korea Exchange. It is the primary measure of the South Korean equity market’s health, equivalent to the S&P 500 in the United States.
Why did the KOSPI crash in 2026?: The KOSPI fell 12% in a single session at the start of the Iran-Israel-US conflict, its worst day on record. South Korea imports around 70% of its crude oil from the Gulf, making the market acutely vulnerable to any disruption to the Strait of Hormuz.Source: Iran-conflict-2026
What is a KOSPI circuit breaker?: A circuit breaker temporarily halts trading on the Korea Exchange when the KOSPI falls more than 8% in a session, to prevent panic selling. During the 2026 Iran conflict, the circuit breaker was triggered twice in four sessions.Source: Iran-conflict-2026
How does the KOSPI compare to the Nikkei and S&P 500 in a crisis?: During the 2026 Iran conflict, the KOSPI fell 12% versus the Nikkei’s 3.9% drop on the same day, and US markets broadly recovered after initial selling. The gap reflects South Korea’s greater direct energy import exposure compared with the US.Source: Iran-conflict-2026
Which Korean stocks fell most during the KOSPI crash?: Samsung Electronics dropped over 10% and SK Hynix fell 12.3% during the KOSPI’s 8%-plus decline in the second major sell-off of the 2026 Iran conflict. Both are among the index’s largest constituents by market capitalisation.Source: Iran-conflict-2026

Background

The KOSPI (Korea Composite Stock Price Index) is the primary benchmark index of the Korea Exchange, listing all common stocks on the market since its launch in 1980. It tracks the Seoul market broadly, serving as the headline measure of South Korean economic health, comparable to the S&P 500 or Nikkei in its respective market.

The KOSPI posted its worst single session on record during the Iran-Israel-US conflict, plunging 12% on the day escalation began, as South Korea’s deep dependence on Gulf oil imports sent investors fleeing. Within two weeks the index fell a further 8%, triggering its second circuit breaker in four sessions; Samsung Electronics shed over 10% and SK Hynix fell 12.3%.

South Korea imports roughly 70% of its crude oil from the Gulf, making the KOSPI acutely sensitive to Strait of Hormuz disruptions. The 2026 shock exposed how a conflict thousands of kilometres away can trigger record domestic losses, forcing regulators to deploy circuit breakers twice in under a fortnight and raising questions about the index’s vulnerability to geopolitical commodity shocks.

How the World Sees Them

Japan

Japan shares South Korea’s Gulf energy dependency and its Nikkei fell 3.9% on the same escalation day. Both markets are regarded as regional bellwethers for how Asian exporters price geopolitical oil risk.

South Korea

South Korea’s economy depends on Gulf energy imports, making the KOSPI structurally exposed to Middle East disruption. The 2026 conflict delivered the index’s worst single-day loss on record, prompting two circuit-breaker halts within a fortnight.

United States

US markets initially sold off sharply on Iran conflict news before recovering on de-escalation signals. The KOSPI’s steeper losses underscored that energy-import-dependent Asian economies bear a disproportionate share of Gulf supply-shock risk.

European Union

European investors tracked the KOSPI’s extreme volatility as a leading indicator of Gulf-exposed market stress. Its 12% single-day collapse preceded broader contagion concerns across export-dependent economies.