Commercially available ZnO substrates drawing attention last years due to perspectives of their utilization in various applications are usually obtained by hydrothermal methods and contaminated by mobile Li or K ions which limit usage of this material in electronics. In this respect, the elaboration of alternative methods of ZnO single crystals obtaining is of great interest. The thermodynamic analysis for use of HCl as a chemical vapor transport agent (TA) for ZnO single crystals growth in the closed growth chambers is carried out in comparison with Cl2 and H2. High density of products for HCl+ZnO interaction, that is favorably for high quality of grown crystals, as well as low temperature dependence of the chemical interaction product densities limiting the rate of ZnO mass transport are predicted. The thermodynamic analysis for use of HCl+H2 gas mixture is carried out also and the possibility of increase in the rate of mass transport is shown. The influence of the growth temperature, density of HCl/HCl+H2 TA and undercooling were investigated experimentally on the rate of ZnO mass transport. It is shown that the use of hydrogen as a TA for ZnO is limited by low structural perfection of the obtained crystals and their destruction during a post-growth cooling because of a strong mechanical contact between grown materials and walls of quartz growth chambers. The use of HCl with a high density up to several atm is favorable for the growth of crystals with a higher structural perfection; however, it is limited by the low rate of mass transport and suitable only at growth temperature no less than 1050 °С. The use of H2 + HCl gas mixture as a TA is useful for 900-1000 °С growth temperature range and also has following advantages: (i) the increase of growth rate in 4-5 times up to 1 mm/day at 1000 °С; (ii) reduction of the growth nucleus density down to 1-3 cm-2; (iii) seeded growth of single crystals densely filling of the growth chamber volume; (iv) absence of the essential attachment effect and destruction of crystals during a post-growth cooling. The structural perfection of obtained crystals having diameter up to 18 mm and substrates prepared on their basis are confirmed by absence of subgrain boundaries and voids in not peripheral areas, by not typically low dislocation density up to 0 mm-2, as well as by infra-red reflection spectra coinciding with theoretical calculations for areas of electron-phonon interaction.