Experimental results of flow pattern for air-water horizontal flow in capillary tubes are reported and flow pattern regime maps are presented at different pressures (from 1 MPa up to 5 MPa). In addition, theoretically based transition criteria for the flow pattern (derived from literature) are presented. The experimental results and theory seem to match each other fairly well. Again, it has been shown that two-phase capillary flow can reasonably simulate a microgravity ''equivalent system'' under normal earth conditions.