Oscillating water column (OWC) type wave energy converters are the most promising candidates to harvest untapped ocean wave energy. OWC front wall opening and power take-off (PTO) damping optimization are very significant for feasible energy extraction. A comprehensive experimental investigation was performed for a bottom-fixed oscillating water column to determine the influence of the underwater opening height of the chamber, power take-off damping and wave steepness on the energy converter efficiency. A broad range of opening heights and power take-off dampings was utilized in physical experiments under various wave steepness values. Water column displacements, velocities and motion behaviors were also examined. Optimal orifice ratios were determined to obtain maximum efficiency under different wave steepness values. Based on the results, the key finding of this study is, for a certain range of wave steepness, optimal damping that should be applied on the system does not only depend on the wave characteristics, but also opening height of the chamber. The motion of water column surface behavior also affects the performance of the converter considerably. (C) 2019 Elsevier Ltd. All rights reserved.