The executive is suspected of committing breach of trust worth 3.03 billion Korean won ($A3.4 million) at an LNG tanker tugboat company he headed before taking over as KOGAS CEO last year.

He is also suspected of taking 280 million Korean won in bribes as CEO of KOGAS from the tugboat firm, an Incheon District Prosecutors' office spokesman said.

Last Friday, Rigzone reported a KOGAS spokesman as saying the world's top corporate buyer of LNG had no knowledge of the indictment and did not foresee a possible management change until he was arrested, as the prosecutors issued the indictment without arresting the CEO.

Jang started his career at KOGAS in 1983 before joining the tugboat company in 2011.

A South Korean district court rejected an application for an arrest warrant against Jang last week for allegedly taking bribes worth hundreds of thousands of dollars.

A spokesman for the prosecutors' office at that time said the office would continue to investigate the case. If he had been arrested, it would have been the second time in 11 years that a KOGAS head had been detained over bribery charges.

Woodside signed a sales and purchase agreement with KOGAS in February to supply about 2.2 million tonnes of LNG over three years from its Pluto LNG plant.

KOGAS also owns 10% of the Shell-operated Prelude floating LNG project in the Browse Basin, which has the capacity to produce at least 5.3 million tonnes per annum of liquids, 3.6MMtpa of LNG and 1.300MMtpa of condensate.

The firm also has a stake in Santos' Gladstone LNG project which will export LNG from CSG in the Surat and Bowen basins.