The assets produce about 20,000 net barrels of oil a day, The Wall Street Journal said. They contain net proved and probable reserves of 66 million barrels of oil equivalent (BOE), of which 61% is actually oil.
"The ExxonMobil properties are an extraordinary fit with our existing, oil-focused core assets, which generate some of the highest margins in the industry," Energy XXI CEO John Schiller said.
The deal will make Energy XXI the third-largest oil producer on the Gulf of Mexico shelf, with interests in seven of the shelf's top 11 oil fields.
Production would rise to about 46,000 BOE a day. That's a gain of more than 77% from its per day average in the quarter ended Sept. 30.
The deal should be completed by Dec. 20.