A novel "On-Stream Supercritical Fluid Deposition" (OS-SFD) process has been investigated in this work coupling the sal gel chemistry and a filtration/compression operation in supercritical CO2 (sc-CO2), for the production of uniform membranes on/in porous ceramic tubular supports. The versatility of this process allows both the direct formation of thin coatings on porous tubular membrane supports but also their internal modification. An attractive on-line control of the deposition process was operated by recording the transmembrane pressure evolution during membrane formation. Silica membranes were directly deposited on macroporous supports (155 mm long alpha-Al2O3, with 200 nm pore sizes) from TEOS derived sols dissolved in sc-CO2 and transported to the tubular support where the condensation/gelation and deposition occurred. The deposition mechanism has been correlated with the sol-gel transition in sc-CO2 conditions and the impact of the deposition temperature, sol formulation and sc-CO2 flow rate on the membrane characteristics (morphology, weight increase and single gas permeance) have been discussed. Supersaturation and precipitation of transported clusters followed by their condensation and gelation were found as key parameters controlling the silica-based membrane design and microstructure/compacity of the silica network. (C) 2013 Elsevier B.V. All rights reserved.