LONDON — An Italian judge ruled on Wednesday that two of the world’s largest oil companies, Royal Dutch Shell and Eni, the Italian company, must go on trial on charges of corruption over a $1.3 billion oil deal in Nigeria.

The judge set a March 5 trial date in Milan for the companies as well as a group of current and former executives, including Claudio Descalzi, Eni’s chief executive, and Malcolm Brinded, a former chief of exploration and production for Shell. No current Shell officials were to be tried in the case.

Both companies have denied wrongdoing, but having such senior or former top executives facing trial is unusual. The court case is likely to highlight the murky dealings of the international oil business, in which large sums of money are sometimes paid to governments for access to resources.

“This is a landmark case,” said Barnaby Pace, a campaigner at Global Witness, a nonprofit group that has conducted its own investigations of the Nigeria case. “This is something of massive concern for the companies involved.”