X-ray computed tomography was used to image two experimental systems containing vapor, liquid, and stainless steel. The first system consisted of a set of test objects designed to incorporate interfaces between the phases at multiple angles. The second system was a film-flow apparatus designed to operate with a film of water in the range of 0.2-0.4 mm thick. The amount of liquid present at selected elevations of both experimental systems was measured from the X-ray transmission data. Less than ten percent variation from expected values was measured for both the stationary objects and the film-flow apparatus. The tomography systems used included a high-energy scanner and a low-energy scanner. The size of a pixel in the reconstructed image ranged from 0.15 to 0.40 mm. The measurement noise was identified as an important factor of the imaging system. The second article in this series will include experimental X-ray CT results for a vapor-liquid contactor and results of the analysis of images produced from simulations of X-ray CT. (C) 2004 Elsevier Ltd. All rights reserved.