Prediction of properties for crude oil blending and distillation is an important activity for refinery planning. Crude fraction properties are measured at laboratory at standard cut temperatures and reported in the so called assays. Owing to the standard cut temperatures differ from the industrial ones, it is required a mathematical procedure to represent the discrete assays’ data as continuous functions. Herein, we present a new methodology based on the Riazi’s equation for TBP curve, the cubic spline interpolation and the Kay’s equation. This new methodology was codified in a VBA-Excel® based program called CrudeExpert which processes assays’ data and evaluates properties for blending and distillation of crudes. The methodology was carried out using the crude assays for Castilla Covenas Blend, South Blend and Cano Limon from ECOPETROL S.A. with successful results for the reproduction of experimental values for density, sulfur content, flash point and carbon residue (Conradson). Likewise, results from CrudeExpert for blending and distillation of the preceding crudes at different cut temperatures were validated with the commercial CrudeManager LE package.