A pressure-tunable series-coupled ensemble of two capillary GC columns is combined with a time-of-flight MS detector for the high-speed characterization of mixtures containing hydrocarbon compounds. The column ensemble consists of a nonpolar 5% phenyl poly(dimethylsiloxane) column and a very polar poly(ethylene glycol) column. The TOFMS instrument uses time-array detection to obtain up to 500 complete electron mass spectra per second. Instrument software allows for automated peak finding and the spectral deconvolution of severely overlapping unknown chromatographic peaks, if their fragmentation patterns are significantly different and if at least two spectra can be recorded between the peak apexes. By adjusting the carrier-gas pressure at the column-junction point, the separations between adjacent peak pairs can be adjusted to enhance the capabilities of the TOFMS detector. The sensitivity of peak-pair separation to changes in junction-point pressure is studied for combinations of alkanes, olefins, and aromatic compounds. When complete separation is required, the use of pressure-tunable column ensembles cannot always provide sufficient control of peak-pair separation for structurally similar compounds. However, complete chromatographic separation typically is not required with the TOFMS detection, and a pressure-tunable column ensemble is very useful for the high-speed characterization of hydrocarbon mixtures.