Royal Dutch Shell and Eni were aware that their $1.3 billion deal for a Nigerian oilfield would result in corrupt payments to politicians and officials, an Italian judge has said.

The two oil majors and former executives are on trial in Milan over alleged corruption in their 2011 deal to secure control of the prized OPL 245 block off the country’s coast. Prosecutors allege that most of the proceeds of the deal went to a company linked with a convicted money launderer and ended up being paid in bribes and kickbacks. Shell and Eni have denied wrongdoing.

The conclusion that they were aware of corruption was made by a judge in a separate case in Milan that resulted in the conviction of two middlemen in…