Nigeria’s Dangote refinery has reduced operating rates at its main gasoline-producing unit by 34% since May 21, raising concerns about fuel supply and export volumes at a time when global oil markets are already under pressure.

Industry monitor IIR Energy said the refinery’s Residual Fluid Catalytic Cracking Unit (RFCCU) is expected to return to full rates by mid-June after repairs to a flue gas slide gate valve.

“Initially, lighter crude being processed resulted in insufficient feed availability for the RFCCU. However, by the end of May, IIR Energy confirmed that the RFCCU was also facing an issue with its flue gas slide gate valve. Repair work on that issue is almost complete,” Reuters quoted IIR as saying in an email.

Dangote refinery have yet to respond on the matter.

Why the RFCCU matters