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More Australians have been implicated in the growing scandal over corruption in the oil industry as the FBI joins forces with British and Australian police to investigate revelations of a huge global bribery racket.
Backed by US Department of Justice anti-corruption prosecutors, the UK National Crime Agency, the Australian Federal Police and the FBI have launched investigations in response to a Fairfax Media-Huffington Post expose of widespread graft and bribery.
Australian engineering giant WorleyParsons has now joined Leighton Holdings' offshore arm and dozens of foreign multinationals facing allegations that they used corrupt agents to win government contracts in oil-rich countries. 
Fairfax Media can separately reveal that a top Australian businessman, Peter Gregg, the chief executive of ASX 100 company Primary Health Care, is the target of a major criminal investigation into a large offshore payment he authorised while chief financial officer of Leighton Holdings.
The revelations place intense pressure on the Turnbull government to respond to corporate corruption scandals with the same ferocity they have attacked corrupt unionists. Labor senator Sam Dastyari and independent Nick Xenophon have revealed they will bring forward to   April a Senate inquiry into corporate bribery and seek to force allegedly corrupt executives to testify.
The inquiry will intersect with the Turnbull government's push to pressure the Senate into reviving the Australian Building and Construction Commission.
"We will use whatever powers are available to us - including the powers of summons and subpoena - to make sure the executives involved have to explain their behaviour to the Australian public," Senator Dastyari said. "The government might only be interested in trade union activity - but the size and scope of what has been exposed by Fairfax is shocking and cannot be ignored."
Justice Minister Michael Keenan said in a statement that taking action against bribery and corporate corruption was "an ongoing task," and that, "the Coalition will continue to explore options to strengthen our laws and our means of enforcing them".
Corporate crime fighters in the US and Europe have urged Australia to ramp up its anti-corporate corruption regime. They say the failure to prosecute Australian firms for bribery may be due to under-resourcing, and that corporate crime investigations are not given priority by Australian authorities.
Fairfax Media can reveal that Mr Gregg is the subject of an active criminal investigation by corporate watchdog ASIC over a $15 million offshore payment.
Leaked documents apparently bearing Mr Gregg's personal signature indicate he authorised a suspect payment to a United Arab Emirates firm, Asian Global Projects and Trading, in   August 2011. The document says the payment was made to guarantee the supply of steel to the Australian construction giant at "preferred and commercially beneficial" prices.
But no steel was ever supplied. The company that received the $15 million is, according to leaked documents, run by an Indian consultant, Mahesh Khemka, who has been involved in money laundering and bribery. Mr Khemka is also closely linked to an Indian businessman who in 2011 was being pressured by Leighton Holdings to finalise a stalled business deal.
Mr Gregg is understood to have paid Mr Khemka's firm the $15 million on the advice of this Indian businessman or his associates, having conducted none of his own due diligence.
ASIC is investigating whether the $15 million payment has breached Australian laws, exposing Mr Gregg to possible criminal or civil prosecution.
Documents also reveal that Mr Khemka was, in the months prior to the $15 million payment, used by other senior figures from Leighton Offshore to launder money and pay $5.6 million in bribes. There is no suggestion Mr Gregg knew of these earlier dealings by his colleagues.
Mr Gregg did not answer a series of questions about whether he conducted any due diligence into Mr Khemka before paying the $15 million. His lawyer sent a statement which said Mr Gregg "denies he has breached any ??? laws" and that he had co-operated with ASIC's investigators.
Rob Ferguson, the chairman of the company of which Mr Gregg is now CEO, Primary Health Care, said he had "every confidence" in Mr Gregg, despite the allegations.
Mr Ferguson's comments stand in contrast to the recent resignation of Australian Securities Exchange chief executive, Elmer Funke Kupper, who quit after learning he was a target of a criminal investigation into an allegedly illegal offshore payment. The payment was also revealed by Fairfax Media and was allegedly made by Tabcorp to secure a Cambodian gaming licence in 2010, when Mr Funke Kupper was CEO of the gaming giant.
In developments outside of Australia, Fairfax Media can reveal that US giants Halliburton and Kellogg, Brown & Root, are among the corporate players embroiled in the Unaoil bribes-for-contracts revelations, part of the biggest leak of confidential files in the history of the oil industry.
A joint Fairfax Media and Huffington Post investigation has revealed the corrupt practices inside a Monaco company called Unaoil, which specialises in bribing officials in oil-producing nations to win government contracts for multinationals.
The latest revelations show Unaoil's campaign of corruption spread across the former Soviet states. Leaked Unaoil files reveal that one of the crooked middlemen, Stefano Borghi, who worked with Unaoil in Kazakhstan, was also working with Australian firm WorleyParsons around 2008.
In conjunction with Unaoil, Borghi paid kickbacks to the senior managers who oversaw oilfield contracts. The oilfields were jointly managed by the Kazakhstan government and Italian international oil company Eni.
In return for bribes, Eni managers leaked inside information and rigged tender committees to assist Borghi and Unaoil's multinational clients.
The leaked files revealed that in 2008, Borghi and Unaoil stood to make hundreds of thousands of dollars if they helped a consortium led by WorleyParsons to win a multimillion-dollar contract.
"In case of award to PARSONS or any third party represented by PARSONS, ECO [Unaoil's British Virgin Islands company] shall be entitled to receive a fee equal to 1% (one percent) of the total price of the portion of the contract awarded to PARSONS," a leaked Unaoil memo states.
Another email shows that, in 2007, a senior WorleyParsons manager used Borghi to find out confidential information in Kazakhstan through "the back door".
At the time, Borghi was bribing a corrupt Eni manager whose job was to oversee several large contracts in Kazakhstan. The manager, Diego Braghi, was leaking sensitive information from a tender committee that was considering whether to award the WorleyParsons' consortium a contract on the Kashagan oilfield.
Managers from the consortium asked Borghi to leak information about their competitors, and to get other forms of assistance from tender committee insiders.
Unaoil regarded WorleyParsons as a company able to pay middlemen huge sums to win contracts. Other firms, including US giant KBR, had scaled back these practices due to concerns over corruption.
"WP [WorleyParsons] do not have any of the constraints that kbr ??? do now and can pay serious fees," Unaoil's memo says.
In the end, for the WorleyParsons manager handling the transaction, this preparedness to do the wrong thing paid off. Worley beat their competitors and won the contract.
In a statement, WorleyParsons confirmed that "Stefano Borghi was an employee of an agent of WorleyParsons."
"At the time the agency agreement was put in place, WorleyParsons had in place rigorous processes to select and appoint agents who provide services to the company," the company said.