Columbia Gas of Pennsylvania keeps the Keystone State gassed up. The company, which can trace its history back to the late 1800s, is a unit of utility giant NiSource that provides natural gas services to customers in western and southern Pennsylvania. All told, Columbia Gas of Pennsylvania serves more than 410,000 customers in 452 communities in 26 counties. Affiliate Columbia Gas of Maryland serves about 32,000 customers in three adjacent Maryland counties. The utilities were previously part of Columbia Energy Group, which was acquired by NiSource in 2000 for $6 billion.