Oil giants Royal Dutch Shell and Eni have voluntarily filed to U.S. authorities internal probes into how they acquired a giant field in Nigeria as the companies seek to fight corruption allegations in Europe and Africa.

The filings, to the U.S. Department of Justice (DOJ) and the Securities and Exchange Commission (SEC), do not mean U.S. authorities are investigating Shell or Eni.

But the move shows the companies are trying to preempt questions from the United States as they face one of the oil industry’s biggest-ever graft trials in Italy, to begin in May in Milan, a pending trial in Nigeria and an investigation in the Netherlands.

The case revolves around the purchase of a huge block off oil-rich Nigeria, known as OPL 245, which holds an estimated 9 billion barrels in reserves.

Italian prosecutors allege that bribes were paid in an effort to secure rights to the block in 2011. A number of top executives from both companies – including Eni Chief Executive Claudio Descalzi and former Shell Foundation Chairman Malcolm Brinded – will face trial.

Under Italian law a company can be held responsible if it is deemed to have failed to prevent, or attempt to prevent, a crime by an employee that benefited the company.

Both companies’ shares are traded on U.S. stock exchanges, putting their foreign dealings in the scope of U.S. authorities.