A high base number calcium sulphonate detergent having a total soap/BN ratio of 0.0530 to 0.0585, preferably 0.0540 to 0.0580, more preferably 0.0550 to 0.0575. The calcium sulphonate detergent has a base number of greater than 350 mg KOH/g as measured by ASTM D 2896-98. The high base number sulphonate exhibits reduced viscosity drift, improved stability and improved catalytic oxidation.