The drifting behavior of PSR B0031-07 is studied using 40,205 periods of high-quality data obtained with the Ooty Radio Telescope, operating at 327 MHz. We confirm the three drift modes centered at slope α = -4.05, -7.78, and -11.46 ms period-1, in the proportion 15.6%, 81.8%, and 2.6%, respectively. Strictly, the three drift modes are not harmonically related. The average subpulse energy and the rms position of the subpulse about the mean slope are both higher in the dominant drift mode, but the average subpulse width is independent of α. The average subpulse profiles in the three drift modes are consistent with relativistic beaming. The average spacing P2 between two subpulses increases monotonically with | α | , contrary to the belief held so far that it is independent of | α | .The drift rate is enhanced at the edge of the integrated profile, which is apparently expected on the basis of the Ruderman & Sutherland model. The average pulse energy during a null is at least 844 times less than that during a burst. This is much higher than the factor of ~100 that has been quoted so far. The integrated profiles in the three drift modes differ significantly from each other. These results (a) enhance the suspicion that the subpulse is the basic unit of radio emission in pulsars, (b) provide a possible model for mode changing in pulsars.