A Shell statement said it was confident that nothing illegal had occurred, adding: "We believe the trial judges will conclude that there is no case against Shell or its former employees".
Anti-corruption watchdog Global Witness says it could be one of the biggest corporate corruption trials in history.
"Eni expresses its full confidence in the judicial process and that the trial will ascertain and confirm the correctness and integrity of its conduct", the Italian firm said in a statement on Wednesday. They deserve to know the truth about what happened to their missing millions.
Besides the two companies, 13 people including Eni CEO Claudio Descalzi and former chairman of the Shell Foundation Malcolm Brinded were put on trial, the sources said. If the deal for OPL 245 represents business as usual for Italy's biggest company, partly controlled by the government, prosecutors were right to investigate and right to bring this matter before the courts.
The deal saw the Nigerian government act as an intermediary between the oil majors and Malabu Oil and Gas, a Nigerian company allegedly controlled by former petroleum minister Dan Etete.
This came a day after the publication of an investigation by Global Witness and Finance Uncovered, which alleged Shell executives and Italian oil company Eni had known the money was being paid to Etete via his front company, and that it would be used to bribe Nigerian officials.
Similarly, Shell and Eni's Nigerian subsidiary, Agip, are among those already being prosecuted in Nigeria. The money had previously been frozen as suspected proceeds of crime at the request of Italian authorities. The Nigerian government, in turn, agreed to pay $1.1 billion to settle Malabu's claims.
"This is not a case involving a few rotten apples", said Nick Hildyard of Corner House. In this case Italy has championed the rule of law over abusive corporate power.