In this article new empirical global depth-distance correction terms for body-wave magnitude are determined using the values of scalar moment M0 in the Harvard CMT Catalogue to calibrate P-wave amplitude-distance curves. Application of new depth-distance correction terms, obtained here, to the ISC dataset shows that estimated mb is independent of distance and focal depth, and provides unbiased estimate of mb, in comparison with other published depth-distance correction terms such as Gutenberg-Richter (1956), Veith-Clavson (1972), and Lilwall (1987). Using Gutenberg-Richter, Veith-Clawson, and Lilwall correction terms, mb for deep earthquakes is systematically underestimated by about 0.1-0.15, 0.3-0.5, and 0.1-0.2 magnitude units respectively. This observation is also a positive test of the hypothesis that a calibration with respect to M0 gives a better estimate of mb. Comparison of the standard deviation of mb values for single events using different depth-distance correction terms shows that the Gutenberg-Richter standard deviations are, on average, larger than those of Veith-Clawson. Lilwall, and this study.