A tall passive flux chamber with a height significantly greater than its horizontal dimensions is proposed for measuring fluxes of volatile organic compounds (VOCs) at the soil surface. The main feature of this tall chamber is the presence of a vertical concentration gradient of the target gas in the chamber. The emission and transport behavior of the target gas in the soil-chamber system are analyzed using the diffusion theory. A mathematical model is developed to estimate the flux from the soil into the tall chamber, providing the target gas establishes a detectable vertical concentration gradient in the chamber. To obtain the data required for calculating flux, only two gas concentrations (C 1 and C 2 ) at two heights (h 1 and h 2 ) within the chamber need to be measured at the end of a short chamber placement time (t p ). To evaluate the applicability of the tall chamber for measuring flux, several laboratory tests have been conducted, using CH 2 Cl 2