The deal includes an option to increase the volume of condensate QatarEnergy exports to Mitsui & Co when additional volumes become available from Qatar's vast North Field liquefied natural gas (LNG) expansion project, the QatarEnergy statement said.

"We are delighted to announce the signing of this long-term sales agreement with one of our strategic Japanese partners, solidifying our decades-long relationship with Mitsui," said Saad Sherida Al-Kaabi, CEO of QatarEnergy and Qatar's Minister of State for Energy Affairs.

Condensates, the by-product of the natural gas production process, are often used in the production of gasoline.

Japanese Prime Minister Fumio Kishida agreed to strengthen energy ties and economic cooperation with Qatar in July when he visited the major gas producing country.

Mitsui & Co said last October it was considering buying a stake in the North Field expansion project as a way to ensure a stable supply of LNG.

Kaabi, in December, said that QatarEnergy was talking to several Asian buyers about becoming "value-added" partners with a stake in the expansion project.

The North Field expansion is expected to boost Qatar's production to 126 million metric tons of LNG per annum (mtpa) by 2027, from 77 mtpa now.

(Reporting by Andrew Mills; Editing by Emelia Sithole-Matarise)