Nido, which is now majority-owned by Thai-based Bangchak Corporation, said the unnamed worker was carrying out support vessel tank cleaning operations in Labuan, Malaysia, supporting the offshore oil facilities.
The worker was undertaking operations for Tiger Oilfield Services on Saturday, April 22 when the accident happened.
The Malaysian police have been notified of the accident and Nido said it would co-operate fully with any official investigation.
Nido will also undertake a comprehensive internal investigation.
"Our heartfelt condolences to the family, friends and colleagues of the deceased," the company said.
Tiger operates bases in Malaysia and Brunei and offers a range of services to the Southeast Asian oil and gas sector, including shipping, base management, marine engineering, and various offshore and vessel management services.
It has been a long-time contractor for the Galoc oil field, providing shorebase and logistics support services under former operator Otto Energy.
It also supported Nido's Baratagan-1 drilling program.
It is not known if Tiger has any role in the drilling of the Galoc-7/ST-1 well, which Nido is undertaking to test a possible extension to the field that is considered vital to extending the life of the operation, which is offshore in the Philippines.
The drilling is being undertaken using the Deepsea Metro I.
Galoc produced a gross 394,000 barrels last quarter, with uptime of 99.9%.
Cargo 55 was lifted in late January giving Nido a net 195,610bbl that sold at $US55.12/bbl.
The field has just two years of life left, unless the Galoc Mid-Area can be developed, however the Galoc-7 well was not the slam-dunk that was expected, failing to resolve issues around reservoir quality and hydrocarbon volume, requiring the sidetrack.
Galoc Mid Area gross 3C resources are 24.5MMbbl, and would add to Galoc's 2C contingent resources of 13.3MMbbl.
Success will see Galoc produce until 2027, but failure means the field is likely to become uneconomic by late 2019.
