Quartz crystal resonators (QCR) coated with various selected sensitive polymers have been investigated for the detection of organic compounds in liquid phase. The targeted organic compounds are tetrachloroethane, trichloroethylene, tetrachloroethane, chloroform, toluene, and xylenes in aqueous solutions. Under optimized experimental conditions using properly designed measurement flow cells and oscillator circuits, proper flow rate, and different coating thicknesses, low detection limits for organic compounds have been achieved. Detection limits as low as 150 ppb and 500 ppb have been achieved with short response time, reversibility and reproducibility using PEA-coated QCR operating at the series-resonant frequency, fs, for tetrachloroethane and trichloroethylene, respectively. Such limits together with the response time clearly indicate that the coated sensors can be used for real-time water analysis. Moreover, using the measured frequency changes, the partition coefficients, KL, of the analyte molecules in the coating/water composite are discussed in order to analyze the sensor mechanism and implement sensor and sensor arrays. Preliminary results on the detection of binary mixtures of analytes are presented and discussed.