A crane has toppled from a methane gas extraction platform, plunging into the Adriatic Sea and killing the operator, Italian energy company Eni said.
The company said the crane also struck a supply boat, injuring two crew members.
The accident happened in international waters, 32 nautical miles off the port of Ancona, when platform infrastructure gave way, the Italian coastguard said.
Coastguard Rear Admiral Enrico Moretti told Sky TG24 TV the operator was trapped in the cabin of the crane, which had been loading a 7-ton canister.
An Italian air force helicopter, fire department divers and coastguard boats searched for the 63-year-old Italian.
The Ansa news agency said the body, still in the cabin, was located by divers 230ft down in the sea.
Eni confirmed the body was found inside the cabin on the seabed near the Barbara F platform.
The energy giant said it is investigating what happened. Italian prosecutors will also conduct an investigation.