The manner in which a sphere behaves when it enters the water from air depends on the rate at which energy is taken from it, and most of this energy is utilized in setting water into motion. The virtual mass is a partial measure of this motion. An investigation of virtual mass for spheres shortly after vertical water entry is described. The spheres used had specific gravities between 1.06 and 16.77 and impact velocities ranged from 21 to 103 ft./sec. The value of the virtual‐mass coefficient was found to be much smaller than had previously been estimated, an average value of 0.08 being obtained. The method used recognizes the dependence ofCDon sphere speed and depth, and makes comparisons only where these parameters have the same value.