The 2021 gathering rule changes the definition of a regulated gas gathering pipeline; more than 400,000 additional miles will be covered by Federal reporting requirements. In the past, most gathering lines were built in low-populated areas, with smaller-diameter pipelines, and with lower pressures of operation. They used to pose a lower risk than transmission pipelines. However, with horizontal drilling and hydraulic fracturing techniques, the volume of gas transported through gathering lines has increased dramatically. As a consequence of larger diameters, higher operating pressures, and several high-profile gas gathering pipeline incidents, the Pipeline and Hazardous Materials Safety Administration (PHMSA) issued a final rule that expands Federal pipeline safety oversight to all onshore gas gathering pipelines. Today, more and more gas gathering pipeline operators are performing feasibility studies to retrofit their pipelines and make them piggable. The purpose is twofold, to make the pipelines run efficiently and provide critical data regarding the condition of the asset, as in-line inspection (ILI) yields the highest per-mile discovery of anomalies.