Over 61 years of earthquake performance of steel transmission and distribution supply pipelines operated by the Southern California Gas Company are reviewed. The seismic record includes 11 major earthquakes with M L ≥ 5.8 and epicenters within the transmission system. An evaluation is made of the most vulnerable types of piping, failure mechanisms, break statistics, threshold seismic intensity to cause failure, and damage induced by permanent ground displacement. The database assembled represents one of the most comprehensive and detailed records of seismic response in a large, complex gas transmission system.