One of the major phenomena occurs during the field trial of synthetic lubricants (SL) is their contamination with mineral oils due to leaking, improper handling and lubrication practices. Effect of this contamination beyond certain percentage generates excess foam, deteriorates air release, clogs the filters etc. which finally leads to damage of the equipment. Hence, estimation of mineral oil in a synthetic lubricant would be of great significance for quality monitoring and maintaining consistent performance. A 1H NMR based method for the estimation of mineral oil in SL based on group-V base oils has been developed. SL includes synthetic esters, phosphate esters, polysiloxane based oil etc. generally used as fire resistant hydraulic fluids, compressor oil, aviation lubricants, refrigeration oils etc. The quantitative estimation of the percentage age of mineral oil contamination has been carried out by unambiguous assignment of characteristic protons of SL over mineral oil using suitable internal standards. In the present study physical blends of pure synthetic esters and finished SL with mineral oil (Gr-II & III) have been studied followed by actual field trial samples. The new method also estimates mineral oil contamination in SL made of mixture of polyalphaolefin (PAO, group-IV) and group-V oils. The method has been validated by known blends. The method is highly repeatable and efficient over 5% (w/w) minreal oil contamination.