King & Spalding has secured the third largest treaty arbitration award in history in a case against the Republic of Kazakhstan.

The $506m (£307m) award, which is also the largest sum ever awarded under the energy charter treaty, was handed down yesterday after three years of proceedings.

The case was brought by King & Spalding on behalf of Moldovan investors Anatolie and Gabriel Stati and their companies, which had invested hundreds of millions of dollars in two Kazakh oil fields whose licenses they acquired in 1999.

In 2010, Kazakhstan seized the assets, after numerous government investigations which the companies said were founded on false accusations of illegal conduct.

A Stockholm arbitration panel found Kazakhstan had violated its international obligation to treat the claimants' investments fairly and equitably.

King & Spalding fielded a team that included global disputes head Reggie Smith, and arbitration partners Ken Fleuriet and Kevin Mohr, alongside a group of lawyers from the firm's Houston, Paris and Moscow offices.

Kazakhstan was advised by Norton Rose Fulbright partner Patricia Nacimiento and former international arbitration head Joseph Tirado, who moved to Winston & Strawn in 2012.

The award comes shortly after another investment treaty tribunal success for the firm, when a team also led by Smith, Fleuriet and New York partner Eric Schwartz secured a $245m (£149m) pay-out for twin brothers Ioan and Viorel Micula against the government of Romania.

That claim centred around Romania's revocation of customs duties exemptions in 2005, which the Miculas said had been agreed when the brothers began developing food and beverage production facilities in the country after the fall of the communist regime in 1989.