Trump uses social media to order 'complete blockade' of sanctioned tankers visiting Venezuela

Legal basis of the term ’blockade’

The use of a blockade is defined as an instrument of war in various international treaties, and is regulated under international maritime and humanitarian law by requiring specific conditions to be met before a blockade is enacted. 

US politicians and legal scholars have opined on President Trump’s apparent assertion that the US would at least partially blockade Venezuelan ports with University of California legal scholar Elena Chachko quoted by Reuters as saying the act of a blockade would raise "serious questions on both the domestic law front and the international law fronts" about whether the US President has the power to order a blockade and the legality of such an act. 

In US domestic law, the US Constitution grants US Congress, not US Presidents, the sole power to declare war. While it is common for US presidents to use military force internationally without a formal declaration of war from Congress, declarations or enactment of "instruments of war" such as blockades would appear to contravene the US Constitution’s terms.

In international humanitarian law, the use of a blockade is addressed in internationally recognised legal texts including the Declaration Respecting Maritime Law adopted in Paris on 16 April 1856, by the Declaration Concerning the Laws of Naval War’s articles 1-21 adopted on 26 February 1909 in London and by the San Remo Manual on International Law Applicable to Armed Conflicts at Sea adopted on 12 June 1994, according to Médecins Sans Frontières. The Paris-based, international medical humanitarian organisation, Médecins Sans Frontières’, Guide to Humanitarian Law defines a blockade as "an act of war that is regulated by international law".

"In order for [a blockade] to be binding to third-party States, it must be effective, and its existence must be officially declared along with a starting date, the territorial geographical limits and a time provided for neutral vessels or aircrafts to be able to leave the area," Médecins Sans Frontières said.

Whether oil tankers already in Venezuela have freedom of movement is questionable, with ship-tracking organisations and news reports documenting a de facto embargo, with vessels remaining in port following a sudden and unannounced seizure of a VLCC by US forces in early December. A new round of sanctions from the US followed the vessel seizure, and a White House press briefing from the US did not rule out further seizures of vessels.

Market reaction

Market analysts Kpler said that the US claim of a forthcoming blockade had not much affected oil prices. 

"The move has so far failed to provide a meaningful boost to oil prices or to overturn underlying fundamentals, largely because the market is two-tiered and even
the sanctioned segment remains crowded," Kpler said.

Kpler’s analysis pointed to a ’limited group of buyers’ affected by any disruption to Venezuelan oil supply, with the broader global market sufficiently supplied to absorb potential shortfalls arising from US actions. 
Venezuela produces around 900,000 barrels per day (b/d) of crude oil and condensate, which accounts for about 1% of total worldwide supply.

"Of the 765,000 b/d exported, about 76% is bound for China, exclusively to teapot refiners, as state-owned firms continue to shun these barrels due to sanctions concerns. The US has taken around 17% [of Venezuelan exports] so far this year – down from a 35% share in 2024 following changes to Chevron’s licence – while the remaining cargoes are shipped to Cuba and a handful of other destinations such as Spain and Italy under the previous licences," Kpler said.

Kpler’s analysts said that the US President’s call for a blockade on sanctioned oil tankers implies that oil bound for the US under Chevron’s licence could continue to flow uninterrupted.

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