Thirty-four heavy oils originating from the four main groups of crude oils around the world-I group: light, low sulfur (30-400 API; S ≤ 0.5% mass); II group: light sulfur (30-400 API; S = 0, 5-1.5% mass); III group: heavy, high sulfur (15-300 API; S = 1.5, 3.1% mass); IV group: extra heavy, high sulfur (150 API, S ≥ 3% mass)-were investigated for distribution of boiling point and molecular weight. The three-parameter distribution model of Riazi and the four-parameter Webull extreme distribution function were tested to approximate the distribution of the heavy oil properties mentioned. It was found that the Weibull extreme more accurately approximates the heavy oil boiling point distribution up to temperatures of 750 • C, and molecular weight distribution up to 955 g/mol. To approximate distribution of higher values extrapolation is needed. Riazi's distribution model was found to be more precise in the extrapolation than the Weibull extreme.