"The final ruling will be delivered to the parties on Thursday, Oct. 2, according to a notification they received last week," one of the sources told Reuters.

Another source said lawyers for state oil company PDVSA had left the country to await the ruling, although it was not immediately clear where they will receive the document.

The International Centre for Settlement of Investment Disputes (ICSID), which is deciding the case, formally has until the end of October to meet a 90-day deadline for a ruling following the close of proceedings on July 28. Pro-opposition Venezuelan daily El Nacional cited a PDVSA source this week as saying Exxon would be awarded between $700 million and $1.2 billion for the takeover of its Cerro Negro heavy oil project and its smaller La Ceiba.

"There are different views and expectations about the valuation amount,” one of the legal sources said. "A figure below $1 billion will be highly favorable to Venezuela, but there are no guarantees of that, and the lawyers of both parties are just hoping for the best."

The company received $908 million from PDVSA in 2012 after a separate decision by the International Chamber of Commerce over a contract dispute linked to the same projects. It was unclear if the ICSID would deduct that sum in its ruling.

Venezuela is facing about 20 cases at the World Bank tribunal after a wave of nationalizations under the late President Hugo Chavez's socialist government.

There has been no official word on the case from either PDVSA or Exxon Mobil. Nor was there any new information on the ICSID website where judgments are posted.

(Writing by Andrew Cawthorne; Editing by Lisa Von Ahn)

By Marianna Parraga