Zinc oxide (ZnO) crystals have drawn attention due to a relatively low price and due to their application perspectives in optoelectronics and photonics [1]. Doping by transitional metals and rare-earth elements is applicable for obtaining new effective light-emitting materials. One of the most cheap and simpler methods for obtaining ZnO crystals with controllable impurity composition varied in a wide range is the chemical vapor transport (CVT) in sealed chambers. The application of chloride compounds as transport agents (TA) can be perspective for obtaining materials homogeneously doped by various metal chlorides in the growth process, as many metals effectively react with chloride. However, the use of HCl as a TA is limited by a very low growth rate of ZnO [2]. Recently, new methods using HCl+H2/CO/C TA mixtures were suggested for ZnO single crystal growth. The increase of growth rate up to 1.5 mm per day has been achieved giving alternative research direction for obtaining ZnO and for its applications [3, 4].  The present investigation is theoretical study of doping efficiency of CVT ZnO crystals, which are doped in the growth process by oxides of various metals. The thermodynamic analysis for composition of ZnO + HCl + MexOy CVT systems in the closed growth chambers was carried out for various oxides (MexOy), including elements of I, II, III groups of the periodic table, transitional metals and some rare-earth elements. The influence of crystal growth temperature, of TA composition, of HCl density, of stoichiometric deviation of growth medium on the pressure and mass transport rate of doping gaseous species were investigated. The advantages and disadvantages of various TAs based on HCl are discussed. The possibility of increase in the doping efficiency by several orders of magnitude for some multivalent metals is predicted, and the application perspectives of various doping materials, as well as optimal growth conditions are summarized.