The determination of two-phase friction pressure drop (TPFPD) in tubes is required by two-phase systems operating under microgravity. However, there is no proper TPFPD correlation for microgravity or reduced gravity, and thus people have to use a TPFPD correlation for normal gravity to estimate TPFPD under microgravity. This paper proposes a TPFPD correlation for microgravity, for which an up-to-data survey of the TPFPD experimental data under microgravity is carried out and a critical review of the published literature regarding TPFPD methods is conducted. Totally, 593 useful experimental data points under microgravity are obtained from 10 references, including 15 with GN(2)-water, 256 with air-water, and 322 with R-12. These data are used to evaluate the existing TPFPD correlations and develop the new TPFPD correlation for microgravity. The new TPFPD correlation is the first TPFPD correlation specifically for microgravity with wide application range. The comparison shows that for microgravity applications it is far better than any existing model. It has a mean absolute relative deviation (MARD) of 20.4% with 56.7% of the sample having a relative deviation within +/- 15%, while the best existing model has the MARD of 25.3% with only 33.4% of the sample having the relative deviation within +/- 15%. (C) 2012 Elsevier Ltd. All rights reserved.