ExxonMobil has temporarily halted operations at its 264,000-barrel-per-day refinery in Joliet, Illinois, following a power outage that affected the facility on Sunday.

The disruption occurred at about 3:30 p.m. local time, with electricity restored roughly three and a half hours later. However, the outage triggered the refinery’s safety flare system and forced a plant-wide shutdown.

ExxonMobil said it was evaluating the condition of the facility, while the cause of the power failure remained under investigation.

Industry data provider IIR Energy said refinery units were being stabilised after the shutdown and projected that the facility could return to normal operations by the end of the week.

The Joliet refinery is an important supplier of gasoline and diesel to the US Midwest. According to ExxonMobil, the facility has the capacity to produce approximately 11 million gallons of the two fuels each day.

The shutdown comes at a time when fuel markets are already facing supply constraints. Disruptions linked to the war involving Iran and attacks on Russian refineries in Ukraine have affected global fuel availability, while strong exports have contributed to tighter US inventories.

The pressure on the US fuel market has also been reflected in diesel prices. The national average price for diesel exceeded $6 per gallon last week for the first time, according to data cited by Reuters.

A prolonged shutdown at Joliet could further tighten fuel supplies and put additional upward pressure on prices if the refinery does not resume normal operations as expected.