Mixtures containing microbubbles or nanobubbles (NBs), as well as their applications, are one of the most interesting research areas in fluid mechanics. In the present study, pressure drops were observed for several types of NB mixtures-NB/water, NB/surfactant, and NB/polymer-when passing through capillary tubes and micro-orifices. Pressure drops of a NB/water mixture agreed with those of water and numerical predictions for a 100-μm orifice, but were lower than both of these results for orifices of 50-μm diameter or less. Agreement was not found between the pressure drops of three NB/surfactant (anionic, nonionic, and cationic) mixtures and those of water or the respective surfactant only in all experimental cases. Moreover, the experimental pressure drops of an NB/polymer (polyethylene glycol) mixture were higher than those of the polymer only. Factors including slip wall, interfacial tension effect, an electric interface phenomenon, and elasticity were examined in experiments and are discussed in this paper. © 2013 Elsevier Inc.