A rapid method for measuring intermediate and heavy fractions in fossil fuels has been developed using HPLC equipment and an evaporative Light scattering detector (ELSD). Measurements at two detector temperatures are sufficient to determine the concentration of vacuum gas oil and residua in heavy oils. Results are comparable to those obtained by GC-simulated distillation (GC-SD). Analysis time is short, and the sample size requirement is small. Good analyses may be obtained with only one or two drops of sample. Since the ELSD detector measures nondistillable molecules directly and GC-SD measures nondistillables indirectly by using internal standards, the ELSD measurements may be the method of choice for measuring residua in heavy oils.