An experimental catchment area was set up by the CEREVE ( Water, City, Environment and Education Research Centre) in the center of Paris, in order to obtain an accurate description of the urban pollutants within combined sewers. Several investigations were carried out between 1994 and 2005 in order to evaluate the aliphatic and polycyclic aromatic hydrocarbon loads entering combined sewers, as well as the pollutant fluxes conveyed by dry and wet weather flows at catchment outlets. Until now, such results have only been considered independently but neither a comparison between imported and exported hydrocarbon loads nor an assessment of the contributions of different sources ( e. g., runoff, dry weather flow and deposit re-suspension within the sewer) to wet weather pollutant loads, have been established. This paper is designed to address these points. The assessment of hydrocarbon loads during dry weather periods underlined a predominant contribution of domestic inputs to the hydrocarbon loads. During wet weather periods, the evaluation of hydrocarbon loads revealed the important role played by in-sewer sediment erosion as a source of wet weather hydrocarbon loads, which contribution ranged from 48 to 55% of the exported loads.