The total base number test (TNB) measures the additives in a motor oil. The higher an oil’s TBN, the better its ability to neutralize contaminants such as combustion by-products and acidic materials. Higher TBN oils neutralize a greater amount of acidic material, which results in longer oil life and cleaner engines. AMSOIL has a large dose of detergents and additives to neutralize acidic contaminants and maximize the life of the engine oil. In tests conducted by independent labs, AMSOIL demonstrated the highest TNB OVER 8 other competitive synthetic motor oils. Read More about the TBN Test and AMSOIL Signature Series Synthetic Motor Oil and here.