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Model studies of the optimal phase matching conditions are performed for the implementation of an optical parametric oscillator (OPO) in the mid-infrared range (IR) based on promising nonlinear crystals, such as: cadmium selenide CdSe, barium selenogallates BaGa4Se7 and BaGa2GeSe6, mercury thiogallate HgGa2S4 and zinc germanium phosphide ZnGeP2 (ZGP). To pump OPOs, it is necessary to use a laser source with a wavelength in the spectral range of 1.9–2.2 μm, since for the combination of physical properties of the listed above nonlinear crystals, it is optimal for achieving the maximum efficiency of parametric frequency conversion. Despite the high values of the effective nonlinear susceptibility and thermal conductivity, the transparency range of the ZGP crystal in the mid-IR range does not exceed 10.4 μm, and the achieved OPO generation wavelength range does not exceed 9 μm in the nanosecond mode. The HgGa2S4 and BaGa4Se7 crystals have lower values of nonlinear coefficients and thermal conductivity and wider transparency ranges and, as a consequence, make it possible to obtain lasing up to a wavelength of 12 μm. When using a BaGa4Se7 crystal, the lasing range can be extended up to 17 μm. The CdSe crystal has the widest transparency range. However, its other parameters do not allow solving the set tasks. [ABSTRACT FROM AUTHOR]