Petroleum heavy distillates find wide application as feedstocks for upgradation through secondary conversion processes. Compositional data on such feedstocks provide useful information to the refiners for selecting processing parameters to achieve product selectivity, quality, and yield. A HPLC method has been optimized to estimate hydrocarbon group types in five lubricating oil base stocks using refractive index (RI) and UV detectors. Data generated at two wavelengths (210 and 254 nm) indicated best results for monoaromatics at 210 nm due to enhanced response and compared well with mass spectrometry data. RI data revealed that saturate content decreases from spindle oil (56%) to heavy oil (42%) which is corroborated by MS data measured for three samples. NMR data exhibited that light oil is more paraffinic (63%) in nature as indicated by branchiness index (0.478). UV data revealed an increasing trend of monoaromatics from spindle (16%) to deasphalted oil (DAO) (20%) and this is supported by MS data, while DAO and heavy oil indicated higher values of diaromatics.