AMSOIL Signature Series 5W-30 Synthetic Motor Oil and nine other synthetic oils were subjected to five industry tests conducted according to American Society of Testing and Materials (ASTM) methodology. Testing examined several important areas of motor oil performance, including resistance to deposit formation, wear protection, high-temperature stability, resistance to acid formation and cold-temperature performance. The overall annual cost of each oil was also compared. When it was all said and done, Signature Series demonstrated the best overall performance and cost-effectiveness. CLICK HERE TO READ FULL STUDY.