An Indonesian ant-corruption court on Friday jailed a third employee of the local subsidiary of US energy giant Chevron Corporation, in a case that has spooked foreign investors.

Widodo, a waste management team leader who goes by one name, was sentenced to two years' in prison over a project to decontaminate 28 plots of land, which prosecutors argued was fabricated and had caused losses to the state.

"Defendant Widodo was found to be legitimately and convincingly guilty of committing a crime of corruption with others" and abused his power to enrich other people or companies, chief judge Sudharmawatiningsih said.

The verdict came after two other employees at Chevron Pacific Indonesia were sentenced to two years' jail this week.

On Thursday the court sentenced manager Endah Rumbiyanti for "failing to carry out her obligations", a lapse which it said unfairly benefited two contractors.

On Wednesday the same court sentenced another manager, Kukuh Kertasafari, for poor oversight of the project.

Sudharmawatiningsih and another judge on the panel of five said Widodo had helped benefit two companies contracted to carry out the project, whose directors have also been jailed.

The decision was not unanimous and all three Chevron cases this week have been peppered by squabbling on the panel, with two judges Friday saying Widodo should be freed.

Prosecutors from the attorney general's office argued that the two contractors had no qualifications or permits.

They also said the land was never contaminated in any case, and the project had cost the state millions of dollars.

Chevron, the country's biggest crude oil producer, denies all accusations and said the clean-up project had been given government approval before it began.

"This project has been approved and tightly overseen by the government, and the success of this project is very obvious," Chevron Pacific Indonesia corporate communication manager Dony Indrawan said.

Chevron lawyer Todung Mulya Lubis said the clean-up was part of a production-sharing contract (PSC) with the government, under which breaches should not be treated criminally and should be settled out of court.

It is highly unusual for the attorney general's office to intervene in such agreements.

The case has sparked concern among foreign energy companies and investors, who have battled fast-changing industry regulations and legal uncertainty in recent years.

Analysts fear it could scare off much-need investment in the oil sector after the country slipped from being a net exporter to a net importer.

The company has said it would support its three employees to appeal to the higher court, and has not ruled out international arbitration.

Another Chevron employee is awaiting verdict in the coming weeks.