NEW YORK - Exxon Mobil Corp said Thursday operations were returning to normal at a gasoline-making fluid catalytic cracker unit at its 238,600 barrel-per-day refinery in Joliet, Illinois following a snag.

In the course of planned maintenance on a diesel hydrotreater, we experienced an issue with the FCC that required the unit to be taken offline for a minor equipment repair, Exxon spokesman Kevin Allexon said in an email.

Operations are returning to normal and all customer needs are being met, he said, adding that the FCC incident occurred late Monday night into early Tuesday morning.

Allexon also said there was no effect on production from a small fire at a storage tank at the refinery early Monday morning. The tank containing residual from process operations caught fire, Allexon said, adding that refinery firefighters contained it.

There were no injuries and no impact to production, he said, noting that an investigation was underway to determine the cause of the fire. (Reporting by Haitham Haddadin; Editing by Lisa Shumaker)