Two-phase flow in mini/micro-channels has been the flow configuration of choice for many cooling applications demanding very high rates of heat dissipation per unit volume. Past research aimed at predicting the frictional pressure drop in mini/micro-channels includes a large number of studies that rely on either the Homogeneous Equilibrium Model (HEM) or semi-empirical correlations. But as the number of published studies continues to rise, thermal design engineers are confronted with tremendous confusion when selecting a suitable model or correlation. The primary reason behind this confusion is limited validity of most published methods to a few working fluids and narrow ranges of operating conditions. The present study addresses this limitation by discussing the development of two consolidated mini/micro-channel databases. The first is for adiabatic and condensing flows, and consists of 7115 frictional pressure gradient data points from 36 sources, and the second for boiling flow, and consists of 2378 data points from 16 sources. These consolidated databases are used to assess the accuracy of previous models and correlations as well as to develop 'universal' correlations that are applicable to a large number of fluids and very broad ranges of operating conditions. (C) 2014 Elsevier Ltd. All rights reserved.