The vessel will be the company's third Very Large Crude Carrier (VLCC) being used to store crude oil. The latest one will join another two located offshore Malaysia, increasing its total storage capacity there to around five million barrels.

PTT was in talks with Socar Trading, the Geneva-based trading arm of Azerbaijan's state energy firm, to sub-lease half of the VLCC, the source said.

Socar will be able to store 1 million barrels of Azeri Light crude and sell it to Southeast Asian customers, he said.

The companies could start storing crude at the end of March if talks are concluded soon, he said.

The lease will probably last a year, with an option to extend it for another 12 months, sources said.

PTT is already leasing two VLCCs - Kadriah 2 and a Titan vessel. The facilities allow the company to buy crude in bulk and split it into small cargoes for its refineries, the source said. It also allows PTT to resell cargoes that its refineries do not need, he said.

PTT has five subsidiaries with a total refining capacity of 1,040,000 barrels per day in Thailand, according to its website.

A Socar official said on Monday it would use a storage tanker for its Azeri Light AZR-E crude blend export in the Asia region.

This will increase SOCAR's exposure to Asian markets after the company also made an investment to build a 650,000 cubic metre oil storage terminal in the UAE port of Fujairah, expected to be operational in about a year.

Socar was looking to increase sales of its Azeri Light crude to Asian customers, particularly on a term basis, to cope with rising production and weak European demand, chief executive Valery Golovushkin said in October.