Pressure fluctuations have been measured in a bubble column using a differential pressure transducer as a function of the superficial gas velocity, both in the air-water system and in water-alcohol solutions simulating the behavior of industrial non-coalescing water-organic mixtures or biological media. Experimental results show that differential pressure sensors can be used to determine regime transitions and to extract regime features using the treatments usually applied to a wall pressure transducer signal (statistical, spectral, fractal, deterministic chaos analyses), although major differences appear between wall pressure and differential pressure measurements in the spectral, fractal and chaos methods. Experimental results prove also the applicability of these methods for identifying the prevailing flow regime and determining the transition points in coalescence-inhibiting systems. If, as expected, the transition is delayed to higher superficial gas velocity in the presence of surface-active agents, this appears to be much more abrupt than in pure water. Thus, the transition region classically observed in water becomes narrower and nearly disappears in the presence of propanol. In this case, the homogeneous regime extends up to a transition velocity corresponding roughly to the starting point of the fully established heterogeneous regime in pure water. (c) 2005 Elsevier B.V. All rights reserved.