A method to generate molecular formula distributions expressed as weight percent abundance of molecular lumps beyond a predetermined threshold of a molecular property for a petroleum stream, the method comprising: obtaining an initial molecular formula distribution within a predetermined threshold of a molecular property for a sample of a petroleum stream comprising measuring the molecular formula distribution using an analytical technique, or generating the molecular formula distribution using a modeling technique, wherein the initial molecular formula distribution comprises a fraction molecular formula distribution for each of a plurality of fractions; identifying a correlation between two or more molecular properties of the initial molecular formula distribution, wherein the two or more molecular properties comprise at least one of hydrogen deficiency, boiling point, molecular weight, molecular fraction, and molecular type, wherein identifying the correlation between two or more molecular properties comprises calculating a coefficient of an equation defining a first molecular property as a function of a second molecular property; extrapolating, using at least one processor, the initial molecular formula distribution beyond the predetermined threshold along the correlation comprising calculating a normal distribution for a first molecular property, or extending the initial molecular formula distribution along a line defined by the correlation to construct an extrapolated molecular distribution; and renormalizing the extrapolated molecular formula distribution based on renormalization data obtained from a measurement of the sample comprising scaling the extrapolated molecular formula distribution and matching a total abundance by molecular type of the extrapolated molecular formula distribution with a total abundance of a measurement of the sample. obtaining an initial molecular formula distribution within a predetermined threshold of a molecular property for a sample of a petroleum stream comprising measuring the molecular formula distribution using an analytical technique, or generating the molecular formula distribution using a modeling technique, wherein the initial molecular formula distribution comprises a fraction molecular formula distribution for each of a plurality of fractions; identifying a correlation between two or more molecular properties of the initial molecular formula distribution, wherein the two or more molecular properties comprise at least one of hydrogen deficiency, boiling point, molecular weight, molecular fraction, and molecular type, wherein identifying the correlation between two or more molecular properties comprises calculating a coefficient of an equation defining a first molecular property as a function of a second molecular property; extrapolating, using at least one processor, the initial molecular formula distribution beyond the predetermined threshold along the correlation comprising calculating a normal distribution for a first molecular property, or extending the initial molecular formula distribution along a line defined by the correlation to construct an extrapolated molecular distribution; and renormalizing the extrapolated molecular formula distribution based on renormalization data obtained from a measurement of the sample comprising scaling the extrapolated molecular formula distribution and matching a total abundance by molecular type of the extrapolated molecular formula distribution with a total abundance of a measurement of the sample.