Abstract: Solute dispersion in multiphase porous media flowWhen a single fluid flows through porous media like soils or geological reservoirs, the transport of contaminants, nutrients, microorganisms, and chemicals is relatively well understood. However, when multiple fluids flow together, these transport phenomena have largely not been considered despite their significance in natural systems. Forces between the flowing fluids and the solid boundaries may create large variations in the local flow rates and form time-varying flow pathways, which can in turn accelerate solute spreading. In this study, we employ extensive computer simulations to propose a new theory on solute spread in systems with two fluids flowing through porous media, offering insights that could enhance our understanding and control of transport properties in natural environments.