(Adds background on possible ICSID ruling)
CARACAS, Sept 25 (Reuters) - A World Bank arbitration tribunal could rule in days that Venezuela must pay between $700 million and $1.2 billion to Exxon Mobil Corp to compensate for a 2007 nationalization, a newspaper said on Thursday.
The International Centre for Settlement of Investment Disputes (ICSID), which is deciding the case, must issue a final ruling by the end of October to meet a 90-day deadline following the close of proceedings on July 28.
The court can also request an extension of 90 days, which would leave the final decision for the end of January.
But pro-opposition Venezuelan daily El Nacional cited a source at state oil company PDVSA saying the ICSID would give a judgment by Monday.
"Preliminary calculations indicate that the total would be between $700 million and $1.2 billion" for the takeover, including Exxon Mobil's Cerro Negro heavy oil project and the smaller La Ceiba project, expropriated by then-President Hugo Chavez.
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 a potential ICSID ruling would deduct that amount already paid.
"If they do not deduct payments already made, the country's finances will be seriously affected," the report said.
Venezuela is facing around 20 cases at the World Bank tribunal.
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.
Should the El Nacional report prove correct, analysts said that would represent a "victory" for Venezuela given that Exxon Mobil is seeking a much larger amount. Two oil analysts who follow the case closely, however, said they had no information that a ruling was as imminent as reported by the newspaper. (Reporting by Caracas bureau; additional reporting by Marianna Parraga in Houston; Writing by Andrew Cawthorne; editing by Matthew Lewis)