The elastic properties of quaternary glass-forming systems within the CaO-MgO-Al2O3-SiO2 composition were evaluated. Their compositions differed by not more than 3 mol% for each component from each other. After melting, the exact chemical compositions were determined using X-ray fluorescence, and the densities were measured by Archimedes method and pycnometer. This property and its dependency upon small variations in the composition are the main focuses of this paper. Experimental elastic properties such as Poisson's ratio and Young's modulus were calculated by measured ultrasound wave velocities (longitudinal and shear) at room temperature. Model calculations of the Poisson's ratios were not in satisfying agreement with the measured results. The experimentally determined data of the Young's modulus values ranging between 87 and 91 GPa were compared to different model calculations, which were mostly smaller than the measured ones, ranging-depending on the model-between 70 and 93 GPa. The effect of MgO was also studied by comparing the glasses with similar compositions without any MgO.