This method is for calculating the UOP Characterization Factorof petroleum oils from API gravity and distillation or viscositydata. Average molecular weight of petroleum oils is estimated fromAPI gravity and distillation data. The UOP Characterization Factor,commonly called K, is indicative of the general origin and natureof a petroleum stock. Values of 12.5 or higher indicate a materialpredominantly paraffinic in nature. Highly aromatic materials havecharacterization factors of 10.0 or less.