An important operational property of glass containers is their mechanical strength. In some cases, the mechanical strength of container glassware is not satisfactory. The reasons of decrease in the strength of glass containers in the process of their production are not always known. The experiments aimed at revealing the causes of instability of mechanical strength of glass containers made of discolored glass. The objects subjected to the experiments are jars, bottles and flasks of colorless glass of different capacities. In accordance with the technical conditions of the standards, mechanical strength of jars, bottles and flasks is characterized by resistance to internal hydrostatic pressure (RIHP). When food is sterilized inside the cans, a fairly high pressure develops due to the fact that the covers are slightly contoured and when the glass container is filled with food, part of the air space remains free. In accordance with the requirements of the standard, jars with a capacity of up to 1000 cm3 must withstand an internal hydrostatic pressure of at least 400 kPa, a capacity of 1000 to 3000 cm3 - at least 300 kPa, a capacity of 3000 to 5000 cm3 - at least 150 kPa. The minimum value of RIHP depends on the type of glass container, its capacity, type of food, etc. Additionally, the jars were tested to the resistance of the compressive force in the directions of the vertical axis to the body (RCFDVAB) and the resistance of the compressive force in the directions perpendicular to the body walls (RCFDPBW). The values of RCFDVAB jars should be not less than 3.00 kN, while the values of RCFDPBW should be more than 1.20 kN. The above values are explained by the fact that the jars are exposed to significant mechanical forces when packaging food products. Test jars, according to the normative documents, allow to determine the suitability of a given batch of glass for the operation. However, this method of determining the mechanical properties of jars does not establish the real level of strength. For this reason, in our experiments, we measured the maximum mechanical strength of jars, i.e., the glassware being tested to RCFDVAB, RCFDPBW and RIHP to their complete destruction. Stability of mechanical strength of the newly-formed glassware has been controlled in the industrial conditions for several years. We revealed a considerable scattering in the values of mechanical strength of glassware. Experimental data show that the maximum value of RCFDPBW jars exceeds the minimum value by 2-3 times. The scattering in RIHP is smaller compared to RCFDPBW. The following regularity was found: the smaller the capacity of jars, the greater their mechanical strength and the smaller the scattering of the results. Analysis of the results showed that approximately 10-15 % of jars with a capacity of 650 cm3 and 1000 cm3 do not meet the requirements of the standard for mechanical strength. We have identified the following reasons that reduce the mechanical strength of glass containers: 1) poor homogeneity of fluid glass; 2) unstable operation of the glass-forming machine; 3) non-uniform cooling of glassware at the stage of final counterblow; 4) poor annealing; 5) various kinds of defects, etc. The measures developed in this study made it possible to stabilize the mechanical strength of glass containers.