Renewable methane could conceivably displace natural gas for use in existing vehicle fleets, reducing greenhouse gas (GHG) emissions as well as emissions of air pollutants like NOx. It is important that policy makers assess the realistic potential for renewable methane. The technical potential for renewable methane production may vary considerably from the volumes that are achievable at realistic levels of policy support. Constraints such as economies of scale, feedstock cost, and distribution all play important roles in determining the cost of production for renewable methane. This study estimates the cost-effectiveness of and additional technical potential for using renewable methane from sustainable feedstocks in France, Italy, and Spain in 2030, relative to its current production. Also estimate the maximum total potential greenhouse gas (GHG) savings for renewable methane, as well as the GHG savings that could be achieved at realistic levels of policy support.