Tracer methods represent techniques commonly used for the characterization and for the monitoring of transport processes in geo-reservoirs (e.g., CO2 storage). The current short communication addresses the development of a conceptual, mathematical and numerical model for a new tracer class (KIS tracers, Schaffer et al., 2013) useful for the characterization of fluid–fluid interfacial areas during supercritical CO2 injection into deep saline aquifers. This tracer type has the potential to quantify the amount of fluid–fluid interfacial areas, important for the quantification of reactions at the fluid interface, which can implicitly lead to optimized injection strategies, a better assessment of the extent of the CO2 plume and of the storage efficiency.