The purpose of this paper is to investigate differences in the perceived relationship of service quality (SERVQUAL)-customer satisfaction between conventional and Islamic banks in the Gulf Council of Arab Countries (GCC) region. We solicited survey responses from bank clients in all six countries of the region. Data reliability tests were applied followed by factor analysis to shortlist individual items of SERVQUAL into few manageable constructs. Nonparametric ranking tests were used to identify levels of importance of constructs. A nonparametric multiple linear regression was employed to model causal effects. The results indicate that customers of the two types of banks perceive SERVQUAL drivers differently. The determinants of the overall satisfaction for the two types, are also different. Implications of the results and recommendations for further research are discussed.