This study aims to measure the effects of bank-specific factors on the efficiency of Pakistan's twenty-seven (27) commercial banks. Efficiency was computed by input-oriented data envelopment analysis approach under CRS (constant return to scale) and VRS (variable return to scale) assumptions. The results revealed that overall inefficiency in commercial banks was to tune of 10 percent and was caused by both managerial incompetence and uneconomical bank's size. However, the uneconomic scale size remained the dominant source of inefficiency at individual banks level, and most of the banks exhibited a decreasing return to scale (DRS) behaviour. Furthermore, efficiency scores were regressed by bank-specific factors using the Tobit regression model. Among the bank-specific factors, Profitability, liquidity, bank size had a significant and positive impact, while market share and Asset quality had a negative and substantial effect on all the efficiency parameters.