Gas transport parameters and X-ray computed tomography (CT) measurements in porous medium under controlled and identical conditions provide a useful methodology for studying the relationships among them, ultimately leading to a better understanding of subsurface gaseous transport and other soil physical processes. The objective of this study was to characterize the relationships between gas transport parameters and soil-pore geometry revealed by X-ray CT. Sands of different shapes with a mean particle diameter (d(50)) ranging from 0.19 to 1.51 mm were used as porous media under both air-dried and partially saturated conditions. Gas transport parameters including gas dispersivity (alpha), diffusivity (D-P/D-0), and permeability (k(a)) were measured using a unified measurement system (UMS). The 3DMA-Rock computational package was used for analysis of three-dimensional CT data. A strong linear relationship was found between alpha and tortuosity calculated from gas transport parameters (T-UMS = root epsilon.D-O/D-P), indicating that gas dispersivity has a linear and inverse relationship with gas diffusivity. A linear relationship was also found between k(a) and d(50)/T-UMS(2), indicating a strong dependency of k(a) on mean particle size and direct correlation with gas diffusivity. Tortuosity (T-MFX) and equivalent pore diameter (d(eq.MFX)) analyzed from microfocus X-ray CT increased linearly with increasing d(50) for both Granusil and Accusand and further showing no effect of particle shape. The T-UMS values showed reasonably good agreement with T-MFX values. The k(a) showed a strong relationship when plotted against d(eq.MFX)/T-MFX(2), indicating its strong dependency on pore size distribution and tortuosity of pore space.