The Illinois Commerce Commission said the expansive project can't come at an unreasonable cost to customers, who have been upset about rising gas bills in recent years.

The utility will resume work on its long-delayed, over-budget program, but the Illinois Commerce Commission has ordered it to prioritize the highest-risk pipes and to bring in an outside monitor for yearly reports.

State regulators will allow Peoples Gas to upgrade aging pipes but not further modernize the city's gas system.