Traders said the tanker, Captain X Kyriakou, was chartered by Swiss-based trading house Vitol earlier in July and had been seen this week off Marsa El Hariga near Tobruk and Benghazi in eastern Libya, the rebels’ stronghold.
The ship can carry up to 1 million barrels but was only partially loaded.
The oil was from storage tanks rather than being fresh barrels from oil fields, the sources said.
“The cargo is the second export from the rebels and it may be the last before Libyan production restarts,” one source said.
Oilfields in eastern Libya have been unable to pump due to the escalating civil war as rebels have sought to oust the government of Muammar Qaddafi since February.
In April, Vitol lifted a cargo of crude oil and delivered it to Hawaii.
AIS ship tracking data showed the destination of Captain X Kyriakou was the Italian island of Sardinia, where it would await further orders, and the estimated arrival date is July 29.
Italian refiner Saras has the only oil refinery in Sardinia.
Saras declined to comment.
A Vitol spokesman and shipowner Athenian Sea Carriers also declined to comment.
Vitol, along with Qatar Petroleum, has been permitted by the US to help market oil for Libya’s Transitional National Council (TNC).
Britain, one of the main foreign players in the campaign to oust Qaddafi, on Wednesday joined the US in recognizing the rebels.
Despite gaining increased international recognition, the rebels are short of funds and their advance has stalled.
France and Britain earlier this week dropped their insistence that Qaddafi leave the country as part of any settlement, a softening of position that indicated a growing anxiety to end a conflict that has now lasted five months.
