Eni chief executive Claudio Descalzi, his predecessor Paolo Scaroni and several managers from Eni and Shell are among those to go on trial, as is Nigeria's former oil minister Dan Etete.
Eni and Shell are accused of handing out bribes during the 2011 purchase of OPL245, an offshore oil block estimated to hold nine billion barrels of crude, for $1.3 billion (1.06 billion euros).
The agreement allegedly saw Nigeria's former president Goodluck Jonathan and his oil minister Etete pocket bribes, according to corruption watchdog Global Witness.
Global Witness said the deal resulted in $1.1 billion being paid into an account in London opened by Nigerian government officials that went directly to Etete. The Nigerian government received only $210 million.
The 2011 deal aimed to end years of litigation over the OPL245 block between Shell and Etete's Oil and Gas Malabu company.
Both companies deny paying bribes.
The trial had originally been set to start in a Milan court in March but was transferred to another chamber due to a large number of pending cases and a new date had been set for 14 May.
The decision to delay proceedings a second time comes pending a ruling on an appeal by Shell set for 12 June concerning the legality of a decision regarding its defendants.
In court Monday, the judge said that it would be prudent to await the outcome of the ruling before launching the corruption trial.
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