Any annulment would be welcome news to Venezuelan government, which is deeply in debt and in recession.
Reuters reported that the World Bank's International Centre for Settlement of Investment Disputes ruling, dated March 9, said "portions of the award" were annulled but did not give a breakdown of figures.
A spokesman for Exxon, Todd Spitler, did not confirm financial details, but told Reuters: "ExxonMobil will continue to evaluate its legal rights and determine next steps."
Venezuela had challenged the 2014 award with various arguments, including that a previous decision from Paris-based International Chamber of Commerce to award Exxon $908 million should be deducted from the ICSID award.
Hugo Chavez, the firebrand socialist leader whose rule was cut short by death from cancer, nationalised a range of oil ventures, including the Cerro Negro heavy crude project and a smaller project called La Ceiba, both operated by Exxon.
Despite its appeal of the World Bank court's initial ruling in the Exxon case, Venezuela's government had hailed that as a success because the company had been seeking compensation of up to $10 billion.
Chavez led a wave of takeovers that also encompassed the electricity, telecoms, metal and agricultural sectors. Many companies deemed the takeovers unlawful, and Venezuela faces more than 20 international arbitration cases.
Supporters of Chavez's nationalisations say he was right to take back control of Venezuela's commodities riches to channel the profits into social programs at home rather than profits for multinational companies.