The vapor pressures of 46 compounds including n-alkanes and their monofunctionalized derivatives, some monoterpenes, as well as chloro- and alkylbenzenes were determined by GLC exploring the Kovats retention indices (KI) technique, primarily in its basic form using two alkane references (GLC-RTKI).The fundamental advantage of the GLC-RTKI method is that it guarantees appropriate selection of alkane reference compounds. Typical relative errors in vapor pressures accompanying this method were below 30% for compounds of low polarity, while for polar compounds (nitriles, alcohols) the errors can reach percentages in the hundreds. In contrast, vapor pressures obtained from the modified Kovats method, relying on reference standards whose functional group matches that of the test compound (GLC-RTmKI), were found mostly within 5% of directly measured values. However, the success of this method is dependent on the availability of reliable vapor pressure data for compounds to serve as reference standards. As our methodology eliminates possible secondary error sources (e.g., data extrapolation, or recalculation from supercooled liquid-to-solid phase or vice versa), we propose that the results obtained are as accurate as is feasibly possible with GLC-RTKI and GLC-RTmKI methods. This study also yielded a novel set of directly measured (static method) data on the vapor pressures of C7C9 alkyl nitriles.