The flutter of 13 panels subject to streamwise inplane load at Mach numbers of 1.57 and 1.96 has been investigated. Panel length-width ratios ranged from 1 to 4.2. The experimental flutter boundary was compared with an analytical flutter boundary for six of the panels. Damping, both aerodynamic and structural, was found to have a pronounced effect on the analytical flutter boundary. The agreement between analysis and experiment was dependent upon how structural damping was introduced in the formulation of the problem.