Eni has completed the sale to BP of a 10% stake in the Shorouk concession offshore Egypt.
BP and Eni first announced the transaction in November.
It leaves Eni with a 90% interest, though that share will drop further when Rosneft completes its acquisition of a 30% stake in Shorouk.
The concession contains the Zohr field, the largest natural gas deposit ever found in the Mediterranean, with an estimated 850billion cubic meters of gas in place.
It is expected to produce gas by the end of 2017.
Signatories included Eni chief executive Claudio Descalzi, BP chief executive Bob Dudley and Egyptian Petroleum Minister Tarek El Molla.
The signing took place in Cairo in the presence of the Prime Minister Sherif Ismail.