It left a port in what was once one of Africa's biggest oil producers late yesterday.
The move has sparked international outcry, with various actors denouncing it as illegal and one country refusing to let the tanker enter its waters. But why is it so controversial, and what are the implications for Libya's future?
What is the background?
Libya has been marred by a brutal civil war since the ousting and death of dictator Moammar Gadhafi in 2011, during which various militant groups and the government have vied for control of the country.
It's been split since 2014 between two rival governments based in the east and the capital city of Tripoli.
Larges swathes of the country remain controlled by dozens of armed groups which are loyal to one or other government, while a few small sections are in the hands of by Islamic State (Isis) fighters.
There's also a UN-backed unity government which was formed earlier this year. It's trying to establish itself in Tripoli and win over the capital's armed brigades, a move that has triggered resistance from some eastern hardliners.
Why is it controversial?
The India-flagged oil tanker Distya Ameya set sail from eastern Libya's Hargia port late yesterday.
This means that the Eastern government has shipped its first cargo of oil since Libya split into two competing authorities around two years ago — defying of previous attempts by Tripoli to prevent such an occurrence.
Why is it illegal?
Several Libyan officials and foreign diplomats have said that sales from the oil shipment would breach UN Security Council resolutions.
Under Libyan law, all oil products must be sold through the internationally recognised National Oil Corporation (NOC) which is based in Tripoli. The Eastern government has set up its own NOC, but this remains distinct from the former.
In 2014, a group which wanted more autonomy in eastern Libya shipped oil from a port there, but US special forces boarded the tanker off Cyprus and forced it to return.
How has the world reacted?
The Tripoli-based government has asked the UN Security Council to blacklist the oil tanker which is thought to be heading for India.
Malta barred the tanker from entering its territories meaning it was forced to dock in international waters.
The US embassy has also said that it's "very concerned" about the attempted sale and reiterated all purchases of Libyan oil must continue to be through the Tripoli-based NOC.
What are the implications?
A successful oil sale would provide a revenue stream for Libya's eastern factions, possibly leading to copycat sales that would shrink the unity government's revenues.
Such a scenario would make it even harder to broker an agreement to end the chaos that has resulted in thousands of deaths and casualties as well as the near collapse of its economy.