This PhD-thesis work is intended for the elaboration of a methodology for risk analysis of accidentai hydrocarbon pollution. This methodology is based on the integration of modelling tools for complex phenomena of subsurface pollution by LNAPL (Light Non Aqueous Phase Liquids). In unsaturated zone, polyphase character ofhydrocarbon pollution is evident while air, water and oil phases coexist. Modelling of multiphase pollution propagation is limited by numerous uncertainties introduced by phenomena ofnonlinearity. Nevertheless, spatial and temporal scale is smaller than in saturated zone. By this, the introduced error for risk estimation of this kind of model is more limited. In saturated zone, pollution is spreading in dissolved form: For this, we use simulation approach hydrodispersive modelling. In this zone, essential transfer direction is horizontal. By this, necessity is imposed to dispose of a spatial analysis tool for risk estimation. For homogenisation of error over the whole distance of a pointwise pollution, influence of the scale where dispersivities have been determined, has to be taken into account. By Geographie Information System, we introduce spatial parameters into hydrodynamic models. Model results are interpreted by spatial analysis to represent spatio-temporal evolution of pollution propagation. ; Ce travail de thèse est destiné à l'élaboration d'une méthodologie d'analyse des risques issus des pollutions accidentelles par hydrocarbures. Cette méthodologie s'appuie sur l'intégration d'outils de modélisation des phénomènes complexes de pollution des eaux souterraines par les LN APL ("Light Non Aqueous Phase Liquids"). En zone non saturée, il s'agit de représenter un écoulement polyphasique puisque les phases air, eau et huile coexistent. La modélisation de la propagation d'une pollution polyphasique se heurte aux limites dues aux nombreuses incertitudes introduites par les phénomènes de non-linéarité. Néanmoins, les échelles spatiales et temporelles sont plus petites qu'en zone saturée. De ce ...