The procedure of estimating the hold-up time in gas chromatography recently presented by Lebron-Aguilar et al. [J. Chromatogr. A, 760 (1997) 219] as the retention of an alkane of zero carbon atoms has been exhaustively tested with packed and capillary columns of various stationary phase types, between 30 and 150°C. Several permanent gases injected have shown that there is not a general rule to decide which is the least retained gas under all circumstances. Results of hold-up times obtained with the new procedure have been compared with those of other well established methods. The conclusion arrived at is that the retention of an n-alkane of n carbon atoms is best described by the expression: t R (n)=A+exp(B+C n D ), and the best estimation of the hold-up time is obtained from that expression for n=0.