Liquid−liquid flows in microchannels are important to microreactors/microfluidic devices that are used to carry out liquid−liquid reactions, extractions, emulsifications, etc. In this work, we report numerical investigations of drop/slug formation and flow regimes for liquid−liquid (oil−water) flow in microchannels. The Volume of Fluid (VOF) method was used to simulate the dynamics of water drop/slug formation in silicon oil, and the predicted drop/slug shapes/lengths were compared with previous literature measurements [Garstecki et al., Lab Chip 2006, 6, 437−446]. The effects of flow rates of water and oil phases (0.019−0.417 and 0.004−0.14 μL/s, respectively), channel size, liquid−liquid distributor (T-junction and Y-junction), and liquid viscosity on liquid−liquid flow regimes and slug lengths were investigated. The predicted drop/slug formation dynamics/slug lengths agreed satisfactorily with the aforementioned Garstecki et al. literature measurements for Qwater/Qoil in the range of 0.1−1.7. However, ...