Deformation and internal circulation of aqueous drops in clear mineral oil are measured in pressure-driven two-phase microchannel flow, using colloidal tracers and drop shape analysis. Drop deformation dynamics, interfacial mobility and interfacial tension during Poiseuille flow and transient elongational flow are analyzed. Using a homologous series of surfactants, the effects of surfactant solubility and concentration are explored, as well as the effect of interface age. Flow kinematics are adjusted by microchannel geometry and relative drop size.