The conjugated dienes if present in gasoline have the tendency to polymerize and cause fouling during various refinery processes. Therefore the conjugated dienes need to be reduced. While the conjugated dienes in gasoline are undesirable, the olefins are desirable and act as octane booster. The selective hydrogenation unit selectively reduces conjugated dienes keeping the content of olefins more or less intact. A method based on HPLC-UV-RI has been reported to simultaneously monitor the conjugated dienes and olefins content in the gasoline range samples. The reported method has the detection level of 0.02 (w/W)% for the total conjugated dienes with respect to 2,4-dimethyl 1,3-pentadiene (DMP). The calibration curve for DMP is drawn in the range 0.2-2.5% (w/W) and the R 2 is found to be 0.9972. The method is also applicable for the estimation of olefins content above 10% (w/W) level with respect to 1-octene. The calibration curve is drawn in the range 10-50% (w/W) of 1-octene and the R 2 is found to be 0.9995.