The Bureau of Mines, as part of a program to improve mine planning and development, is currently investigating the effects of pillar load transfer, which can impact mining operations within a multiple- seam configuration. A comparative study was performed at two separate mine sites. The objective of this study was to compare two mines, each affected by this pillar load transfer mechanism, and to show how this interaction affected underground workings by installing and monitoring underground instrumentation . At mine site a, where the overburden was 1,000 ft, the innerburden thickness was less than a pillar width (40 to 45 ft), overlays of the mine layout show pillars were not superpositioned, excessive roof to floor convergence was measured, and pressure readings indicated pillar core loading only. At mine site b, the overburden was approximately 555 ft, the innerburden thickness was approximatley 105 ft, overlays of the mine layout show pillars were superpositioned, minimal roof to floor convergence was measured, and pressure readings indicated a skin loading only.