Oil/water/air data are reported for vertical flow in a 0.026 m i.d. pi
pe. Nine flow regimes were identified by visual/video and pressure tec
hniques and flow regime maps presented. A relation for determining the
transitional boundary between oil and water dominated regimes was pre
sented. Total liquid and individual phasic liquid holdup data in the f
orm of a complex series of curves showing the influence of input liqui
d flow rates, gas rates and flow pattern were presented. Pure liquid h
oldup data obeyed existing models for the water system. A new relation
was presented for the oil system. Using these models the total liquid
holdup against oil/liquid ratio was quantified for annular flow patte
rns. Pressure loss data are presented as complex curves showing the in
fluence of input fluid rates and flow patterns. Results show that the
pressure loss went through a minimum as the gas rate was increased in
a similar way to that observed in two-phase flow. A qualitative explan
ation of the data was presented for annular flow patterns based on the
formation and interaction of the various annular/annulus films presen
t.