This paper discusses the factors that affect the occurrence of coal pillar bumps at the Olga Mine. These factors have been broken down into two categories--in situ, and those that are related to the mining process itself. The in situ factors include those conditions that exist prior to mining, such as variations in lithology and overburden, presence of jointing, the composition and the physical properties of the rock, and the original stress field existing in the coalbed and adjacent strata. The mining-related factors include the mining sequence, changes in stress in the coalbed and adjacent strata during mining, rates of convergence, and the pattern of failure of the coal and adjacent strata. The factors determined to have the greatest effect on bumping were the overburden, the lithology of the roof and floor rock, and the physical properties of the rock.