Diallyl disulfide (DADS) and diallyl trisulfide (DATS) are major allicin-derived organosulfur compounds associated with biological activity and sensitivity to processing conditions. This study aimed to quantify DADS and DATS in commercial garlic products using gas chromatography–flame ionization detection (GC-FID) and to evaluate the effects of product formulation and processing on their concentrations. Fresh garlic, marinated garlic, garlic oil, tinctures, powders, dragees, and oil- and granulate-based capsules were analyzed. The GC-FID method showed excellent linearity for both analytes (R² = 0.9999). Marked differences were observed among the investigated product types, and selected pairwise comparisons indicated statistically significant differences (p < 0.05). Garlic oil contained the highest concentrations of both compounds, with mean DADS and DATS levels of 179.98 and 102.26 mg/g, respectively. In contrast, the mean concentrations in all other product groups were substantially lower, reaching 0.01068 mg/g for DADS and 0.03649 mg/g for DATS. Oil-based formulations showed markedly higher DADS concentrations than powder- and granulate-based products, whereas DATS was relatively more dominant in powder-based formulations. Marination and thermal processing were associated with reduced diallyl sulfide levels. These findings demonstrate that the investigated commercial garlic products differed substantially in their DADS and DATS content, mainly depending on formulation and processing. The pronounced variability observed among the investigated commercial products highlights the need for improved analytical standardization and quality control of garlic-based products.