Updated

A corporate bribery trial billed as the biggest in history is opening in Milan against oil companies Shell and Eni as well as former and current executives, all charged in a $1.1 billion scandal to win control of one of Nigeria's most lucrative oil blocks.

The heft of the two oil companies makes the trial the biggest ever, according to anti-corruption campaigners. They also say it is unprecedented that Eni's current CEO, Claudio Descalzi, remains in his post while he faces such serious charges.

Descalzi is one of 13 individuals charged in the case involving the 2011 purchase of the OPL245 block, along with his predecessor, two former top Shell executives, a former Nigerian oil minister, and a series of middlemen and advisers. The companies themselves are also corporate defendants.