[en] Photochemical transformation of petroleum hydrocarbons, n-alkanes, polycyclic and monoaromatic hydrocarbons under the influence of UV radiation of a mercury lamp have been studied by chromatography and UV spectroscopy. It has been established the kinetic regularities of the formation of abovementioned hydrocarbons within the irradiation up to 90 min at 2x10''15 photon/s UV-light intensity in various concentrations of crude oil up to 5000 ppm on the water surface. A mechanism of possible photochemical processes is discussed. Photochemical degradation of crude oil in an aqueous medium is one of the physicochemical processes, taking place under the influence of UV part of solar radiation and constitutes about 10% of oil conversion in case of oil film on the surface of seawater. Degradation of crude oil occurs under the influence of various physical factors - including the effects of temperature, wind speed, chemical composition and the biological state of seawater. Simultaneous influence of the abovementioned factors makes it very difficult to clarify the mechanism of degradation process of crude oil. Taking into account the abovementioned features of photochemical degradation, it is expedient to study model system consisting of crude oil and distilled water. This work is devoted to the study of photochemical processes under the influence of UV radiation in model system of crude oil-water