Two petroleum resids and their products from catalytic upgrading were characterized by high-temperature simulated distillation using gas chromatography (HT-SimDis GC) with a capillary column. The atmospheric equivalent boiling points (AEBP) determined by the HT-SimDis GC method in this work reached an end point of 847 degrees C (1557 degrees F). This method successfully analyzed the AEBP distribution of an atmospheric resid and a vacuum resid as well as their products from catalytic hydroprocessing. The analysis of the AEBP distribution vs. reaction temperature revealed that catalytic upgrading not only produced lighter fractions but also created desirable changes in the remaining >540 degrees C fractions. For the runs over a sulfided Co-Mo/Al2O3 catalyst, the yields of products with BP range of 540-700 degrees C remained almost constant when the reaction temperature was within 350-400 degrees C but decreased monotonically with further increasing reaction temperature up to 450 degrees C. At 450 degrees C, the 450-540 degrees C fraction was also converted. The extent of catalytic hydrodesulfurization over Co-Mo/Al2O3 catalyst increased with temperature from 350 to 450 degrees C.