The men were found guilty of conspiring to corruptly obtain payments by supplying confidential information about contracts for five oil and gas projects in Iran, Egypt, Russia, Singapore and the United Arab of Emirates between 2001 and 2009. The total value of the contracts was approximately £70 million, the Serious Fraud Office (SFO) said.
Andrew Rybak, 55, from Newbury; Ronald Saunders, 64, from Hook; Philip Hammond, 57, from Brussels; and Barry Smith, 71, from Hindhead, were convicted of the offences at Southwark Crown Court on Wednesday.
The convictions followed a joint investigation by the SFO and the City of London Police. The investigation started in April 2008 and was prompted when a company bidding for a contract in Singapore reported that Rybak had made a "suspicious approach" offering information about the process in return for money, the SFO said. Further evidence of suspected corruption was then discovered in relation to the other contracts and identified Rybak, Saunders, Hammond and Smith as being involved, it said.
The men were charged with offences of conspiracy to corruption in September 2010 after investigators had searched mobile phone data, travel records and information in e-mails in a trawl for evidence. A fifth man, who had been charged, was not convicted of any offence on Wednesday after the jury failed to reach a verdict.
Under the Criminal Law Act individuals are guilty of conspiring to commit an offence if they carry out actions "in accordance with their intentions" that they had agreed with others that "will necessarily amount to or involve the commission of any offence or offences by one or more of the parties to the agreement, or would do so but for the existence of facts which render the commission of the offence or any of the offences impossible".
Under the Prevention of Corruption Act a person can be jailed for obtaining or accepting, or agreeing to obtain or accept, "any gift or consideration as an inducement or reward for doing or forbearing to do ... any act in relation to his [employer's] affairs or business, or for showing or forbearing to show favour or disfavour to any person in relation to his [employer's] affairs or business".
"Corruption in business life diminishes society," Richard Alderman, Director of the SFO, said in a statement.
"[This] outcome makes it clear that it will not be tolerated. The investigation is an excellent example of collaboration between the City of London Police and the SFO. Each of us used our particular powers and skills, combined in a complex case with significant international links," he said.
Rybak, Saunders, Hammond and Smith will be sentenced on 30 January. The SFO said it would begin "confiscation proceedings". Rybak, Saunders and Hammond had shared hundreds of thousands of pounds between them for their part in the exchange of information regarding bids for the contracts, the SFO said.