Four different spices were packaged either under 100% nitrogen or using ambient air, and then gamma-irradiated at different doses. The essential oils of the original spices and of those irradiated were obtained by hydrodistillation. Changes to the essential-oil compositions due to irradiation and effects of packaging were detected and compared by using comprehensive two-dimensional gas chromatography (GCxGC). The use of GCxGC provided better separation and more reliable results. It enabled ready detection of some peaks that coeluted with other peaks in the first-dimension column (D-1). Differences in detected peaks were observed after irradiation of samples packaged under ambient air, with additional peak(s) noted. Two peaks appeared after irradiation of aerobically packaged rosemary, black pepper and thyme, and one peak increased in relative abundance in the samples. No changes in these three peaks were noted after irradiation of samples packaged under 100% N-2. These three essential-oil components were identified by using GCxGC quadrupole time-of-flight mass spectrometry (Q-TOFMS). The changes after irradiation were mainly due to packaging type, and no effect of the irradiation dose was observed in the study.