Capacitance void fraction sensors were used to obtain void fraction measurements in Vertical two-phase water-air flow in a small diameter tube (9.53 mm). Measurements were obtained at 1 - g and mu - g conditions. Comparisons were made between the void fraction values obtained at both gravity conditions by matching the flow rates obtained at mu - g conditions. It was found that the average void fraction values were comparable for the bubble, transitional how (slug-annular flow at mu - g, and churn flow at 1 - g), and annular flow regimes. The slug flow regime showed a slightly higher overall average of about 10% at mu - g conditions. The distribution coefficient, Ca, which takes into account the flow regime and the void fraction profile was found to be 1.25 for bubble and slug flows at mu - g, and 0.61 and 1.17 for 1 - g bubble and slug flows, respectively. This suggests that a ’flatter’ void fraction profile exists for slug flow at 1 - g as compared to mu - g. The value of 0.61 for bubble flow agrees well with the typical values obtained by averaging the ’saddle’ shape void fraction profile typically seen at 1 - g.