North Asian refiners have stepped up purchases of U.S. crude as an alternative to Middle Eastern barrels that may no longer be able to exit the Strait of Hormuz, where the chokepoint remains effectively closed amid a continuing stalemate between the United States and Iran.

At least four Asia-based refiners bought U.S. crude volumes this week alone, traders told Reuters on Friday.

Tanker traffic – and shipping traffic as a whole – at the Strait of Hormuz slumped further this week, according to observable transits with AIS positioning switched on. The strait is the world's most important oil transit chokepoint: roughly one-fifth of global petroleum liquids consumption normally moves through it, according to the U.S. Energy Information Administration.

With the Hormuz standoff unresolved, Asian refiners are searching further afield for alternative supply, as tight fuel markets and sky-high refining margins encourage refinery runs wherever sufficient crude is available. The United States has grown into one of the world's largest crude exporters since Washington lifted a four-decade ban on oil exports in December 2015, giving Asian buyers an established alternative supplier – albeit one an ocean away.

Among this week's deals, GS Caltex of South Korea bought 2 million barrels of Mars crude – a medium-sour grade produced in the U.S. Gulf of Mexico that many Asian refineries can run in place of some Middle Eastern barrels – from Shell for delivery in November at a premium of $13–14 above the October Dubai benchmark, according to Reuters' trade sources.

Cosmo Energy Holdings, one of Japan's biggest refiners, also bought Mars crude, from commodity trader Trafigura. Eneos Corp, Japan's largest refiner by capacity, purchased 2 million barrels of West Texas Intermediate (WTI) crude from Trafigura for November delivery, priced at a premium of more than $10 per barrel above the October WTI price.

CPC Corp, Taiwan's state-owned energy company, acquired 2 million barrels of WTI via a tender at a premium of around $8 to $9 per barrel to Dated Brent, according to Reuters' sources.

The longer supply line is a built-in trade-off of the pivot westward: voyages from the U.S. Gulf Coast to North Asia typically take six to seven weeks, compared with roughly two to three weeks from the Persian Gulf, extending the lead time before replacement cargoes arrive.

Further south, some state-held Indian refiners are also seeking spot crude as term deliveries remain constrained by the ongoing crisis in the Middle East and its key oil chokepoint, the Strait of Hormuz. India is the world's third-largest oil importer and consumer, and its refiners have historically sourced a large share of their crude from the Middle East.

Mangalore Refinery and Petrochemicals Limited (MRPL) and Hindustan Petroleum Corporation Limited (HPCL) are looking to buy a combined 6 million barrels of crude oil via spot tenders, Reuters reported earlier this week, citing tender documents it had seen.

By Tsvetana Paraskova for Oilprice.com.