The oil industry has been revealed to be tangled in corruption and bribery on a global scale, involving companies from the United States, United Kingdom, Europe, Asia and Australia reportedly worth billions of dollars.

A leak of confidential documents unveiled government contracts worth billions of dollars were allegedly awarded on the basis of bribes, fronted by company Unaoil, Fairfax Media reported.

After obtaining hundreds of thousands of leaked emails and documents, the news agency discovered the extent of corruption to be widespread, with the commodity required nearly everywhere in the world  – labelling it the ‘world’s biggest bribe scandal’.

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According to the six-month investigation between Fairfax Media and The Huffington Post, Unaoil charged clients multi-million dollar fees for its operatives to then bribe officials in oil-rich countries to help these clients score government contracts.

Unaoil reportedly played on the fears of large Western oil companies that they cannot win the contracts without its help.

At the pinnacle of payoffs is the Ahsani family, with sons Cyrus and Saman heading the Monaco company, the report said.

Ten years ago, the family was said to have 190 million in euros between them in cash, shares and property.

The report said that the bribes were paid on behalf of multi-international firms including Britain’s Rolls-Royce, US giant Halliburton, Australia’s Leighton Holdings and Korean heavyweights Samsung and Hyundai.

The leaked files allegedly declared some representatives of these companies believed they were hiring genuine lobbyists, while, others merely turned a blind eye.

In one instance, Unaoil allegedly paid at least $25 million in bribes, securing the support of a number of Iraqi officials – including former Deputy Prime Minister Hussian al-Shahristani – to secure Iraq’s lucrative oil fields.

However, since 2007 Unaoil has been certified by anti-corruption agency Trace International, bringing question to the value of international accreditation.

Ata Ahsani, a spokesman for the Unaoil, was quoted as denying any wrongdoing, saying the company ‘absolutely’ does not bribe officials.