With the passage of Euro 6, and the recent U.S. introduction of new CO₂ limits for heavy-duty trucks and buses, vehicle and engine manufacturers are facing a daunting challenge. Compliance with these regulations requires significant financial investments in new technologies, all designed to increase fuel efficiency while decreasing emissions. But, to remain competitive, manufacturers cannot pass along these costs to fleet owners. One solution to this problem is the opposed-piston engine. This engine, which has been optimized by Achates Power, was once widely used in a variety of applications including aviation, maritime and military vehicles. After overcoming the architecture's historical challenges, the Achates Power opposed-piston engine now delivers a step-wise improvement in brake thermal efficiency over the most advanced conventional four-stroke engines. In addition, with the elimination of parts such as the cylinder head and valve train, it is also less complex and less costly to produce-making it even more appealing to manufacturers. After a brief overview of the opposed-piston architecture's inherent efficiency benefits, this technical paper features detailed performance and emissions results of a multicylinder Achates Power opposed-piston engine configured to meet current commercial truck requirements. Presented for the first time in Europe, these results demonstrate the engine's ability to: Significantly improve fuel efficiency over the best diesel engines in the same class. Comply with Euro 6/U.S. 2010 emissions standards The discussion also includes an in-depth analysis of the opposed-piston, multi-cylinder test engine's indicated thermal efficiency, friction and pumping losses as well as a road map for achieving 47.6 percent best-point brake thermal efficiency (BTE), which translates to 46.6 percent cycle-weighted BTE on medium duty engine, while the same technology results 51.5 % best point BTE, and 50.4 % cycle weighted BTE on a heavy duty engine. Furthermore, the technical paper provides a vibration analysis between the Achates Power opposed-piston architecture and the inline six-cylinder, four-stroke engine, which dominates the medium- and heavy-duty truck market.