Abstract In this investigation, we report the study of an optical device for the measurement of hydrostatic pressure in fluids. The device studied is a sensor based on a dielectric optical resonator in the form of a capillary that confines the light in its interior through the phenomenon of total internal reflection. In the analytical study of the sensor, the excitation of the azimuthal modes WGMs inside the resonant cavity is considered, so that their sensitivity to changes in the hydrostatic pressure was analyzed as a function of the displacement of wavelengths of resonances in the cavity.