This paper discusses an actual problem of Estonian oil shale open casts: the technological limit of overburden thickness. The allowable principle stripping operation schemes for walking draglines at Estonian oil shale open casts are presented. Computer modelled methodology is worked out for evaluation technological limit of overburden thickness in Estonian oil shale open casts and in similar conditions As the result of the study if is possible to declare: the technological overburden thickness is 16-27 m for dragline ES15/90 and 20-37m for dragline ES30/120 depending on geological and mining conditions. The methodology allows mining engineers to calculate and evaluate open cast mining conditions and cutting parameters for Estonian oil shale open casts or similar conditions and lends to solving one of the key problems in long range planning, the limit of surface mining. If helps to prepare the documentation and diagrams of stripping operations.