Stray gas migration as a result of hydrocarbon extraction has caused environmental concern and is receiving widespread attention. Natural gas migration in the subsurface can have environmental implications when gas components (e.g., methane, longer-chained hydrocarbons) dissolve into shallow groundwater or pass through groundwater systems to the atmosphere. Because of the complexity of the subsurface systems and the parameters affecting stray gas migration, systematic quantification is difficult, particularly in field studies. To focus on key processes of gas migration, laboratory experiments offer a controlled environment to collect data which can be applied to field and modeling efforts. In this study, methane was injected into an intermediate-scale (150 × 150 × 2 cm3) two-dimensional flow cell packed with saturated homogeneous or heterogeneous unconsolidated sands. The impact of active methane leakage versus stopping of leakage was investigated. High-resolution, visualization techniques coupled with high-frequency water sampling at multiple depth-discrete intervals allowed for understanding of coupled methane migration and mass transfer. Results show that methane dissolution is affected by heterogeneity, active versus inactive leakage, and multicomponent mass transfer, prolonging the longevity of both free- and dissolved-phase methane in the subsurface. Findings highlight the importance of considering geology, hydrogeologic conditions, and multicomponent mass transfer in gas migration systems at the field scale.