Allen & Overy (A&O) and Allens have scored lead roles on a multibillion-dollar oil refinery project in Vietnam – touted as one of Asia's most important energy developments.

The Nghi Son Refinery and Petrochemical Complex, Vietnam's second refinery, will be built on a 400 hectare site in Thanh Hoa province, south of Hanoi, and will process 200,000 barrels of oil per day in the first phase – approximately 40% of Vietnam's fuel requirements.

The owner and developer of the project, Nghi Son Refinery and Petrochemical Company (NRSP), is a joint venture between Japan's Idemitsu Kosan Co, which holds a 35.1% stake, Kuwait Petroleum International, which also has 35.1% ownership, state-owned Vietnam Oil and Gas (PetroVietnam) which owns 25%, and Mitsui Chemicals which owns 4.8%.

Last month NRSP signed a $5bn (£3.2bn) contract for the engineering, procurement and construction (EPC) of the project with a consortium of contractors, subject to raising the capital from a core group of lenders. The remaining $4bn (£2.6bn) required for the project will come from investor equity.

A Government Guarantees and Undertaking Agreement (GGU) was also signed between NSRP, its investors and the Vietnam Government, which provides legal, taxation and currency regimes, arrangements for works that will be contributed by the government as well as guarantees in relation to sales of fuel products.

Australia's Allens advised NRSP on the EPC contract alongside in-house counsel, with Perth-based partner Michael Hollingdale leading a team and working closely with the firm's Vietnam office. Allens also acted for the developer on its negotiations with the government for the GGU, with Hanoi partners Hop Dang and Bill Magennis instructing a group of lawyers in the Vietnamese capital.

Philip Cornwell, a Sydney-based project finance partner at Allens, is currently representing NRSP as it looks to raise the remaining capital for construction.

Meanwhile, A&O is acting for the lenders, which includes export credit agencies and commercial banks from around the world. The firm declined to comment.

"This will be the largest project financing in Vietnam in the 20 years I have been here," said Allens' Magennis.

"In addition to its significance to Vietnam, this project holds importance regionally, with long-term agreements with Kuwait and Japanese companies for the supply and purchase of products."