The Ahsani clan (from left) Saman, Cyrus and Ata, who run the Monaco-based oil company Unaoil at the centre of worldwide bribery scandal.

The Unaoil company at the centre of a global oil industry bribery network appears to be owned by a New Zealand shell company.

A Fairfax Media investigation of Unaoil obtained a document which shows the "wiring diagram" for the network of Unaoil entities through which giant multi-national companies channelled bribes to corrupt officials in oil-producing countries including Iran, Iraq and Libya.

After a six-month investigation across two continents, Fairfax Media (publisher of the Sydney Morning Herald, The Age and Stuff) revealed on Thursday that billions of dollars of government contracts were awarded as the direct result of bribes paid on behalf of firms including British icon Rolls-Royce, US giant Halliburton, Australia's Leighton Holdings and Korean heavyweights Samsung and Hyundai.

The investigation centres on a Monaco company called Unaoil, run by the jet-setting Ahsani family.

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* Unaoil bribery scandal: The worldwide players

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* Unaoil bribery scandal: The Australian angle

The leaked evidence of its own internal email cache demonstrated that the multimillion-dollar fees Unaoil takes from its clients were funnelled into an industrial scale bribery operation which further entrenches corruption among the powerful few.

The wiring diagram appears to show Unaoil is owned by UNA Energy Group Holding of Singapore, and that in turn is owned by UnaEnergy Trustees based in Auckland.

But the Auckland company is just a link in the chain, and it is owned in turn by Fleetwood Trustees, based in the tax haven of St Kitts and Nevis.

The Auckland company has three directors, but two at least appear to be trusts specialists who make a living providing professional services to others.

They are Monaco-based Lesley Ann Fogden from Rosemont Monaco SAM, which calls itself a "multi-family office services company, which manages trusts, corporations, foundations and other legal structures and their underlying assets for multiple wealthy families".

The Auckland company's only New Zealand-based director is Richard Gordon Wilson, who is a foreign trusts expert from Jackson Russell Lawyers, a Shortland Street law firm.

Wilson said: "UnaEnergy Trustees Limited is a trustee of a trust established for UNA Energy, and holds the shares in a holding company based in Singapore".

"We just act on instructions from an outfit in Monaco which runs family offices for wealthy clients," Wilson said.

That organisation was Rosemont, for which Jackson Russell sets up New Zealand trust arrangements.

"They are a very reputable organisation of English professionals," Wilson said.

He said his involvement was minimal, and he was not involved with the day to day operations of UNA Energy.

"The rest of the story is news to me," he said.

"I am not at liberty to talk without clients' instructions."

New Zealand has a substantial foreign trust industry. Trustee companies based in New Zealand can be used to own companies and assets located overseas. Income those assets earn is not taxable in New Zealand.

When he was in Parliament, former Green Party co-leader Russel Norman fought for a tightening up of regulations around the use by foreigners of New Zealand trusts and companies, which were easy to set up.

Now as executive director of Greenpeace, Norman is an opponent of big oil.

He said the New Zealand Unaoil link would put the spotlight back on the New Zealand trust industry.

"It will certainly draw attention to all of the problems that have been previously identified in the way New Zealand companies and trusts system still works, and the very weak regulation around it," Norman said.

New Zealanders were proud of the country's reputation as being corruption free. "It's part of our identity," he said.