The high-pressure equilibrium phase diagram of tin is investigated, and the crystal structure of Sn II at 98 kbar and 25°C is shown to be body-centered tetragonal with a=3.70 Å, c=3.37 Å, c/a=0.91, and with two atoms per unit cell. The linear compressibility of white tin is given at 25°C up to the high-pressure transformation at 92 kbar, and the latent heat of the transformation is measured as 225 cal/g-atom.