The purpose of this study was to confirm the existence of acoustic emission (AE) Kaiser effect (KE) in Estonian oil shale (OS), and compare the respective data obtained about working mine pillars. The KE of acoustic emission, a phenomenon with a potential for in-situ stress estimation, can be used for quantifying the damage levels of pillars, and possibly even to measure the state of stress within a pillar. The main role of measurements is to confirm estimated stresses, as the estimation is quite simple in regions of sedimentary rocks. The performed tests showed that the Kaiser effect did exist in oil shale material, at the same time, the low material strength also lowered the feasible stress limit for KE-based stress measurements. Tests were made with inspection of the formula for changes of long-term rock durability in the Estonian oil shale formation. On the basis of the obtained results, the AE method can be used to estimate the long-term rock durability for pillars in conditions of Estonian oil shale mines.