Capillary gas-liquid two-phase flow occurs in increasingly more modern industrial applications. The existing relevant data are limited and are inconsistent with respect to the reported flow patterns and their transition boundaries. A systematic experimental investigation of two-phase flow patterns in microchannels was the objective of this study. Using air and water, experiments were conducted in circular microchannels with 1.1 and 1.45 mm inner diameters, and in microchannels with semi-triangular (triangular with one corner smoothed) cross-sections with hydraulic diameters 1.09 and 1.49 mm. The gas and liquid superficial velocity ranges were 0.02-80 and 0.02-8 m/s, respectively. Overall, flow patterns and flow pattern maps using gas and liquid superficial velocities as coordinates, were similar for all the test sections. The discernible flow patterns were bubbly, churn, slug, slug-annular and annular. The obtained data were compared with existing experimental data. They were also compared with relevant flow regime transition models and correlations, generally with poor agreement.