  B^0-anti-B^0 flavor oscillations have been studied in 20.7 fb-1 of e^+e^-
annihilation data collected in 1999 and 2000 with the BABAR detector at
center-of-mass energies near the Upsilon(4S) resonance. The event sample
consists of one B^0 meson fully reconstructed in a hadronic decay mode, while
the flavor of the recoiling B^0 in the event is determined with a tagging
algorithm that exploits the correlation between the flavor of the heavy quark
and the charges of its decay products. By fitting the time development of the
observed mixed and unmixed final states, the B^0-anti-B^0 oscillation
frequency, Delta_md, is determined to be 0.519+/- 0.020+/- 0.016 ps^{-1}.
