tion of BTEX in real water samples using HS-SPME combined with GC with flame ionization detection (FID) has been optimized in order to achieve the best selectivity and sensitivity. The optimized procedure has been applied in a VOCs monitoring program. Several compounds (Fig. 1) have been determined in water samples from the Mediterranean Sea and estuaries. BTEX data from samples from two different estuaries: Salinas Santa Pola – river Segura, and Cullera – river Jucar, both in the Mediterranean sea have been used in order to study the influence of temperature and precipitation in the area during a period of three years. For this aim, a chemometric study based on Principal Components Analysis (PCA) and Principal Component Regression (PCR) has been performed.