Hybrid organosilica membranes were successfully prepared using bis(triethoxysilyl)ethane (BTESE) and applied to reverse osmosis (RO) desalination. The organosilica membrane calcined at 300 degrees C almost completely rejected salts and neutral solutes with low-molecular-weight. Increasing the operating pressure led to an increase in water flux and salt rejection, while the flux and rejection decreased as salt concentration increased. The water permeation mechanism differed from the viscous flow mechanism. Observed activation energies for permeation were larger for membranes with a smaller pore size, and were considerably larger than the activation energy for water viscosity. The organosilica membranes exhibited exceptional hydrothermal stability in temperature cycles up to 90 degrees C. The applicability of the generalized solution-diffusion (SD) model to RO and pervaporation (PV) desalination processes were examined, and the quantitative differences in water permeance were accurately predicted by the application of generalized transport equations. (C) 2012 American Institute of Chemical Engineers AIChE J, 59: 1298-1307, 2013