The Spanish firm said on Monday it would have to pay the sum to an unidentified LNG producer following a ruling by the International Court of Arbitration of the International Chamber of Commerce in a dispute over a retroactive price adjustment.
The opposing party was seeking around $1.28 billion, Endesa said in its financial report in October.
State-owned QatarEnergy didn't immediately reply to a request for comment outside of usual office hours.
An Endesa spokesperson declined to comment. Earlier on Wednesday, Endesa Chief Executive Jose Bogas said the other party in the dispute was from Qatar, Nigeria or Algeria.
"We are still calculating the impact but I believe a big part of it - something around $500 million - could be recouped with the new price mechanism on the same contract in two years and a half," Bogas said, speaking on the sidelines of an event of Endesa's parent company Enel (ENEI.MI).
Qatar is the world's leading LNG exporter at a time when competition for LNG has increased following the war in Ukraine. European countries in particular have rushed to offset dwindling pipeline imports from Russia with gas supplied by sea.
Thanks to its extensive LNG infrastructure, Spain has emerged a key European hub for Europe's LNG imports.
