A versatile equation is used to describe the cumulative weight, mole, or volume fraction (x) with various properties (P) of petroleum fractions (eq 1), with P* = (P {minus} P{sub 0})/P{sub 0}, where P denotes the boiling point (T{sub b}), specific gravity (S), refractive index parameter (I), or molecular weight (M). For a given property, the value of B is approximately constant for most crude oil and gas condensate samples: T{sub b}(B{sub t}{approx}1.5), S(B{sub s}{approx}3), I(B{sub I}{approx}3), and M(B{sub M}{approx}1). Therefore, only two unknowns must be determined for a given property distribution: A and P{sub o}. The fitting procedure is straightforward and can be performed with linear regression of the form Y = C{sub 1} + C{sub 2}X where Y = In P* and X = In In (1/(1 {minus} x)). The proposed procedure has been tested on more than 80 crude oil and condensate samples from around the world. Once the fit has been made, the eq 1 can be applied as a continuous distribution in terms of a probability density function.