The octane number indicates the "knock resistance" of the fuel. It is determined in line with the RON (Research Octane Number) under defined conditions with precisely defined test engines. Regular petrol with 91 RON has the lowest value, premium grade petrol has 95 RON, super grade 98 ROZ and newer "Super Plus" fuels are 100 RON at the top end. (Ver comentario). With petrol, the higher the octane number, the higher the spontaneous combustion temperature is and the lower the tendency to cause knocking during combustion (spontaneous combustion temperature: regular petrol 450-550°C, super 480-700°C).