This study investigates the impact of financial reforms, bank characteristics, and time trends on the performance of the Vietnamese banking sector under the assumption that ownership can result in a divergence of technologies utilised by different bank groups (including state - owned, private, and foreign banks), and the fact that these groups may respond differently to the same environmental variables . By combining a meta - frontier analysis with double - bootstrap two - stage DEA the authors analyse the impact of en vironmental variables on bank efficiency across separate groups operating under different technologies. Accordingly, this paper, firstly, employs ownership as an ex ante rather than an ex post factor as used in all earlier studies when examining the influe nce of this environmental variable on bank efficiency. Using data for Vietnamese banks covering the period 2007 - 2012 our results show that the performance of bank groups is significantly different, and that state - owned banks are more efficient and have a s maller technology gap to the meta - frontier in comparison with foreign and private banks. Moreover, these different bank groups react dissimilarly to a number of variables, for instance , state - owned banks have a negative, while private banks have a positive , relationship to the loan to asset ratio.