Presented is an investigation into the modeling of limit cycle oscillation (LCO) behavior of an experimental transonic airfoil aeroelastic configuration using a frequency-domain harmonic-balance (HB) computational fluid dynamic (CFD) approach. The aeroelastic model has a single structural degree-of-freedom in pitch. Wind-tunnel wall interference effects are included in the CFD model. A wind-tunnel resonance is observed near the flutter onset and LCO conditions. © 2003 by Jeffrey P. Thomas, Earl H. Dowell, and Kenneth C. Hall. Published by the American Institute of Aeronautics and Astronautics, Inc.