The adsorption of tetra ethyl lead on the surface of the quartz crystal of an electronic microbalance and the deposition rate on the crystal as a function of light intensity and pressure during the photolysis of tetra ethyl lead (TEL) were measured. Although the deposition rate was controlled by a gas-phase reaction, a secondary surface reaction controlled the delineation of the deposit. Oxygen reduced the amount of TEL adsorbed and increased the photodeposition rate by a secondary surface process. Carbon was detected in the photodeposit from pure TEL but a photodeposit obtained in oxygen did not contain either carbon or oxygen.