An experimental investigation on oil-air two-phase flow through a straight horizontal plexiglass pipe within 40mm inner diameter was conducted.The superficial velocity ranges of oil and air were 0.05—0.612m8226;s-1 and 0.024—50.64m8226;s-1

respectively.The ambient temperature was maintained throughout the experiments.The frictional pressure drop multiplier of two-phase flow was expressed using the Lockhart-Martinelli parameter correlation in accordance with typical flow pattern

but the modification factor C in the correlations was defined afresh according to flow conditions.New predict correlations for pressure gradient in accordance with typical flow patterns were proposed and the mechanisms of pressure drop production were analyzed for each flow pattern.The proposed models gave good agreement with the experimental data.