Beta Regio is an area of rifting and volcanism on Venus, constituting a topographic rise. A shield volcano, Theia Mons, lies near the center of the region and is surrounded by several radially oriented rifts. We use Magellan altimetry, gravity, and synthetic aperture radar data of the area to constrain some subsurface parameters. First, we derive hoop strain. Using altimetry data and a fault dip angle derived from the split crater Somerville, we determine the extension in the rifts surrounding Beta Regio. We then derive the hoop strain accommodated by the rifts from the extension in these rifts. Except near Theia Mons, the hoop strain follows the shape expected from a mantle upwelling. The difference near the volcano, we believe, is due to volcanic infilling. We then model three observable quantities, the newly derived strain along with gravity and uplift, using two separate modeling techniques, one for the strain and uplift and another for the gravity. The model results show that the data are consistent with the view that a relatively low density contrast region now exists below Beta and has caused the uplift and rifting in the region. ¿ 1999 American Geophysical Union