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

According to Reuters, the filings, to the US Department of Justice, DOJ, and Securities and Exchange Commission, SEC, do not mean US 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 alleged 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.

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

Shell and Eni, on behalf of subsidiaries, in 2010 entered deferred prosecution agreements with the DOJ over separate Nigerian corruption allegations.

Those pacts dismissed charges after a certain period in exchange for fines and an agreement to fulfill a number of requirements. They concluded in 2013 and 2012, respectively.