In this study, three physical models of oscillating water column (OWC) with a scale of 1:60, three submergence depths, and six wave frequencies were applied to investigate the offshore OWC performance in different conditions. A factorial analysis of variance was conducted to compare the main and interaction effects of the back wall height, structure submergence depth, and wave frequency on the OWC performance. Experimental results show that 5 cm and 10 cm back walls improved the OWC efficiency up to 118 and 183 percent, respectively, and the submergence depth of 0.25 chamber length is most beneficial. Based on variance analysis, all three factors were influential on the OWC performance, but the effects of wave frequency and back wall height were highly significant. Using eta squared as the measure of effect size, the wave frequency and back wall height accounted for 50% and 13% of the total variability in the output power, respectively. Among the interaction effects, back wall height × frequency had the highest effect on the output power. A Bonferroni test for this interaction showed that combinations of two back walls with the two highest frequencies tested (1.11 Hz and 0.95 Hz) have the highest output power.