The corporation had its start as the Alabama Gas Company which was acquired by the Southern Natural Gas Company in 1937 and the Birmingham Gas Company, which had been operating since 1879 before merging into the Birmingham Railway, Light & Power Company in 1898. The two were merged into the Alabama Gas Corporation in 1948. The corporation, which handled distribution, was spun off from Southern Natural in 1953. A holding company, Alagasco Inc. was created in 1974, headquartered in Birmingham. It was renamed as the Energen Corporation in 1985.
In 2014 Energen sold Alagasco to the Laclede Group for $1.6 billion. At the time of its sale, Alagasco provided energy to approximately 425,000 homes and businesses with 11,230 miles of mains and more than 12,000 miles of service lines. It operated divisions in Anniston, Birmingham, Gadsden, Montgomery, Opelika, Selma, and Tuscaloosa. Laclede changed its name to "Spire" in 2016 and rebranded its Alagasco operating unit under that name beginning in September 2017.
- Behel, Sandra and the 150 Committee (2002) Energen Corporation. Images of America Series. Mount Pleasant, South Carolina: Arcadia Press. ISBN 9780738514611
- Tomberlin, Michael (April 7, 2014) "Energen selling Alagasco to St. Louis company for $1.6 billion." The Birmingham News
- Rebman, Stephanie (September 11, 2017) "Spire's Alagasco rebranding takes hold this month." Birmingham Business Journal
- Alagasco website