A Rock-Eval 6 dataset of 66 samples from the Cape Phillips Formation in the Canadian Arctic region was studied to investigate source rock characteristics and petroleum generation potential. Bulk geochemical characteristics and thermal decomposition behavior of the samples indicate an initial generation potential close to 700 mg HC/g TOC and show an unusually low onset T-max temperature for petroleum generation. This led to an examination of possible T-max suppression due to a large amount of high-molecular-weight heavy oil and bitumen derived from the early breakdown of kerogen in the samples. Application of a numerical method based on kerogen decomposition kinetics allows for the numerical removal of thermal evaporative products of oil and bitumen adsorbed in the sample without requiring additional pyrolysis experiments or solvent extraction treatments of sample replicates. The removal of the adsorbed hydrocarbon from samples increases the T-max value up to 17 degrees C. The estimated petroleum in the sorption phase varies from 1 to about 9 mg HC/g rock, depending on the total organic content (TOC) and maturity, and is the main form of the total oil yield in this area. The corrected T-max-HI cross-plot suggests an onset of petroleum generation around 435 degrees C of T-max, consistent with the general consensus for a normal marine source rock in this region. The constructed kinetic model shows a maximum of 75% transformation ratio (TR), and most samples show TR ranging from 10 to 50% in the early oil generation window on Cornwallis Island. This reconstructed source rock thermal decomposition model in a geological time scale indicates the onset of massive petroleum generation at a temperature of 120 degrees C, and the maximum transformation ratio of 75% corresponds to a temperature of 140 degrees C over geological time.