Marine Engine Oil were traditionally classified after their kinematic viscosity. Marine Engine Oil is a mostly valid criteria for the quality of the oil as long as the oil is made only from atmospheric distillation. Today, almost all Marine Engine Oil are based on fractions from other more advanced refinery processes and the viscosity itself says little about the quality as fuel. CCAI and CII are two indices which describe the ignition quality of residual fuel oil, and CCAI is especially often calculated for Marine Engine Oil. Despite this marine fuels are still quoted on the international bunker markets with their maximum viscosity (which is set by the ISO 8217 standard - see below) due to the fact that marine engines oil are designed to use different viscosities of fuel.