The photocatalytic decomposition of HCCl3 was studied in a fully irradiated photoreactor (FIP) by varying the concentrations of (a) chloroform, (b) dissolved oxygen and (c) titania, as well as (d) the local volumetric rate of energy absorption (LVREA). Fully irradiated conditions are achievable when all the particles along the light path ’see the photons’. In order to compute the VREA (average value of the LVREA), the radiative transfer equation (RTE) was applied to the reactor and solved using a simplified radiation model. Model parameters, i.e., optical properties, as well as the boundary condition for the RTE were obtained experimentally. Initial rate data of the chloroform decomposition showed that, within the studied range of process variables and under fully irradiated conditions : (i) The reaction rate is of first order with respect to [HCCl3], zero order with respect to [O-2] and about one-half-order with respect to the LVREA inside the reactor and (2) : The effects due to catalyst concentration are fully accounted for within the LVREA dependence.