The flow regimes and pressure drop in a slit microchannel with a height of 164 μm and width of 10 mm are studied experimentally. The boundaries between the regimes are precisely determined using the developed procedure. The homogeneous flow model and the separated flow model are considered for determining the frictional pressure drop. Experimental data are compared with theoretical models. For the homogeneous flow model, the Dukler correlation gives good agreement with experimental data with a mean absolute error of 12%. A new correlation, which describes the experimental data with a mean absolute error of 8.1%, is proposed for the homogeneous flow model. For the separated flow model, the Hwang and Kim correlation gives the best agreement with a mean absolute error of 12.8%. The dependence of the pressure drop in the film flows (annular and stratified regimes) on the mass gas quality has been investigated. It is shown that the minimal pressure drop for the film flows is achieved in the stratified regime; thus, it is the most promising for the use in technical applications.