 This paper examines the relationship between market concentration and bank efficiency in the Middle East and North African, MENA, region. It uses a sample of 225 banks from 18 countries over the period 2006 to 2020 in tests whether there is a significant correlation between the two variables. The authors find that market concentration has a positive effect on bank efficiency, which is stronger for Islamic banks than conventional ones. Additionally, they observe that the effect of market concentration is more pronounced during the COVID-19 pandemic, as well as for government-owned banks. This article was authored by Miroslav Mativ, Mohammed Usman Tariq and Ahmad Sayouni.