The static fermentation of coconut water sucrose by Acetobacter xylinum was tarried out at initial pH's of 3.0, 4.0, 5.0 or 6.0. Cellulose was produced at the surface, and its production was most favourable at pH's 4.0 and 5.0. These pH values also allowed for optimal bacterial growth. Oxygen concentration profiles were measured with microelectrodes at different cultivation stages, and steep profiles were obtained with penetration depths between 50 and 100 mu m. A substrate penetration depth analysis confirmed the hypothesis that the first stage of the fermentation is entirely oxygen controlled. Diffusion calculations showed, however, that at a later stage sucrose becomes a limiting substrate also, which was confirmed by the decrease in cellulose production rate over time. The effective diffusion coefficient of oxygen in deactivated cellulose pellicles was measured with microelectrodes, and a value of 1.4 x 10(-9) m(2)/s was obtained under all investigated conditions. The oxygen flux was 5.9 x 10(-6) mol/m(2).s, while a significantly higher value of 9.1 x 10(-6) mol/m(2).s was obtained at pH 4.0.