The refinery, located in western part of Russia, would hold maintenance of isomerisation and catalytic reforming units from Oct. 1 until Nov. 15, the source said.

"There will be a large-scale maintenance of the reforming and isomerisation. There will be no high octane, while A-76 (low octane gasoline grade) will emerge for exports," a source said.

Kirishi usually produces more than 200,000 tonnes of gasoline per month. Sources said it was expected to produce more than 100,000 tonnes of A-76 gasoline grade per month during the maintenance.

The plant did not immediately respond to a request for comment.

(Reporting by Reuters; Editing by Edmund Blair)