Hybrid silica membranes have demonstrated to possess a remarkable hydrothermal stability in pervaporation and gas separation processes allowing them to be used in industrial applications. In several publications the hydrothermal stability of pure silica or that of hybrid silica membranes are investigated. To gain deeper insight into the mechanism of hydrothermal stability of silica-based membranes we report a comparison under identical conditions of the gas permeation performance of silica (TEOS), hybrid silica (BTESE) and Zr-doped BTESE (Zr-BTESE) membranes before and after hydrothermal treatments. First, a fast and straightforward hydrothermal stability test at 100 degrees C was applied to screen these membranes. The BTESE and Zr-BTESE membranes maintained their excellent performance after this test, though the TEOS membranes lost their selectivity. Second, hydrothermal tests under water gas shift (WGS) conditions were performed at different temperatures. No significant changes in permeance and selectivity were observed for BTESE derived membranes after a hydrothermal treatment at 300 degrees C. Surprisingly, a large reduction in carbon dioxide permeance was observed for Zr-BTESE hybrid silica membranes after a hydrothermal treatment at 200 or 300 degrees C, resulting in a significant increase of the H-2/CO2 permselectivity from 12 to 35. (C) 2017 Elsevier B.V. All rights reserved.