Small rivers are highly important elements of fresh water and sanitary-domestic supplies, local ecosystems functioning, thus they are essential for the environmental and civil safety of local areas. Chemical composition of the upper parts of rivers determines the chemical composition of waters downstream. The article represents the results of long-term researches of the Tysmenytsia upriver and its tributaries. The peculiarity of this area is its location within one of the oldest European oil recovery centers. According to the results of this research, the spatial changes of mineralization and the main components of chemical composition were established: the main ions, nitrogen compounds, petroleum products and phenols. The upper tributaries of the Tysmenytsia are characterized on average by hydrocarbonate calcium-magnesium composition with mineralization of 0,450 g/dm3, and the waters of the main river streambed by sulfate-hydrocarbonate sodium-calcium composition with mineralization of 0,207 g/dm3. The waters of the Tysmenytsia upper part on average contain nitrites (NO2-) of 0.12–0.20 mg/dm3, nitrates (NO3-) of 1.8–3.4 mg/dm3, ion ammonium (NH4+) of 0.21– 0.24 mg/dm3, petroleum products of 0.27-0.66 mg/dm3, phenols of 0.007- 0.010 mg/dm3and characterized by a COD value of 7.74-13.6 mgO2/dm3. This article also provides explanation of spatial changes of chemical composition of waters, conducts comparison with the composition of other Carpathian mountain rivers. Analyzed waters refer to the 2ndclass of water quality. Established facts and analysis of their causes are potent scientific base of forming civil protection measures and environmental safety of investigated areas.