This paper presents an experimental method for liquid level detection in gas-expanded liquids by the sound speed and amplitude. Volumetric expansion of acetonitrile and 2-propanol as a function of CO2 pressure was determined between 298-333 K and 0-6 MPa. Propane expansion of 2-propanol was done up to 393 K and up to V/V-0 = 8. It was clearly demonstrated that this technique is useful also for multiphase detection with high accuracy and for obtaining accurate speed of sound values without calibration. The paper also presents an experimental method for gas composition sensing. The speed of sound and sound attenuation as a function of hydrogen concentration in CO2 and in propane atmosphere at ambient conditions were measured to obtain information whether an acoustic technique could be an alternative method for the determination of H-2 solubility in liquefied gases and in gas-expanded solvents. (c) 2006 Elsevier B.V. All rights reserved.