During growth the colorless SrLaAlO4 and SrLaGaO4 crystals grown on seeds of the [1 0 0] orientation by the Czochralski method undergo a change and become yellow and green with increasing oxygen pressure. To understand this phenomenon the enthalpies of formation of SrLaAlO4 and SrLaGaO4 were determined and thermodynamic calculations on the dissociation of the compounds as a function of temperature and oxygen pressure were carried out and the role of crucible material was considered. It was found that (1) the partial pressures of species containing AI, Ga and Sr ions depend on the oxygen pressure in the growth chamber, (2) the calculated equilibrium oxygen pressures at T-melt are 7.26 x 10(-8) atm and 2.66 x 10(-7) atm for SrLaGaO4 and SrLaAlO4, respectively, and (3) the colorless and light-yellow crystals grow at an equilibrium oxygen pressure lower than about 5 x 10(-4) atm while the green-colored crystals grow at an oxygen pressure higher than 5 x 10(-3) atm in the growth chamber.