Grazed pastures and cultivated lands are major agricultural emission sources contributing greenhouse gas (GHG) emissions as the result of N2O emissions derived from fertilizer deposition and animal excreta.  While soil carbon storage is also affected by land use and soil aggregate structure. Subsurface migration of gas occurs by diffusion and the ability of a soil to migrate the gas is expressed as soil-gas diffusivity (Dp/Do) which is a function of soil air-filled porosity (?) and gaseous phase tortuosity (?) that vary with soil texture and structure. Agricultural soils are structurally aggregated and are frequently subjected to compaction and tillage resulting in alteration to structural arrangement but with little effect on texture. Soil Dp/Do behaviour in a well-structured soil cannot be expressed using a simple linear, power law or combined linear and power law functions due to the preferential gas movement paths arranged in between and/or through the soil aggregates. A comparative study between Currie’s (1960) and Taylor’s (1949) methods was performed to provide computational insight into selecting an appropriate method for calculating Dp/Do in agricultural soils. Taylor’s (1949) method was chosen for further analysis of the soils in this study. A new Two-Region model was developed, aimed at parameterising the Dp/Do of aggregated soils, and tested against repacked samples from two Sri Lankan agricultural soils. This Two-Region model clearly distinguished tortuosity effects on gas movement with respect to density and textural variations, outperforming previous models. The fitting parameters (?1, ?2, ?1 and ?2) varied correspondingly with soil density, and the weighting factor (w) clearly distinguished the boundary between two regions (Intra aggregate and Inter aggregate) of structured soils. The model developed will be of interest to those seeking to model gas diffusivity of GHG emissions within soils.