Reservoir fluid characterization by high-temperature gas chromatography (HTGC) extends the range of single carbon number (SCN) groups in oil analyses by temperature programming up to 450 degrees C. However, the reliability of HTGC analyses is questionable for two main reasons: first, possible pyrolysis of the injected oil inside the GC column which could induce overestimation of light and intermediate fractions; and second, possible incomplete elution of heavy fractions, which in turn would induce under-estimation. The former has been treated in the first paper of this series,(1) which focused on predicting the pyrolysis temperature of n-alkanes (nC(14)H(30)-nC(80)H(162)) at GC conditions. The latter is the focus of this second paper which introduces a gas chromatography migration and separation model for the n-alkane range nC(12)H(26)-nC(62)H(126) in an HT5 column, using as main input the in-house distribution factors derived from isothermal GC retention time measurements. On the basis of the developed model, the concentration and velocity of the above n-alkanes were determined at every point and time throughout the GC column, for typical temperature-programmed analyses. Retention times were then predicted, and validated against experimental values, with an overall relative error within 2%. This study gives an insight into the components' behavior throughout the GC column, allowing preliminary assessment of elution, by proposing a new approach for determining the non/incomplete elution of every component by introducing: the degree of elution, defined as the amount of component which has been eluted in relation to the amount injected. Thus, the degree of elution of each of the heavy n-alkanes studied in this work: (nC(12)H(26)-nC(62)H(126)) has been calculated for a typical temperature program. This new approach can be applied, in order to determine the analytical conditions required for ensuring maximum elution of a given component, with the possibility of improving the practice of HTGC by optimizing the separation process.