This paper presents a new and fast method to measure the in situ coal cleat compressibility in a vertical well. Traditional coal cleat compressibility is measured in a lab using small coal samples placed in a cell for its exposure to methane, temperature, pressure and stress representing the in situ conditions. This test takes about one year to complete, and coal heterogeneity and fragility make selection of representative samples difficult. While testing coals for permeability, borehole storage coefficients up to 100 times larger than expected were observed. This anomaly suggests a coal cleat compressibility effect and provides a foundation to develop a new method to measure coal cleat compressibility from borehole storage analysis.To assess the reliability of the method, 52 measurements were compared against internationally published lab data. The range of variability considered from both data sets presented a good correlation which validates the results applied from conventional well testing. This is a good result given that coal cleat compressibility changes with depth, coal rank and gas content. This simple method, developed from permeability testing technology, should help engineers understand coal permeability variations with gas drainage, stress, and geomechanical changes.