Complications during the intraocular use of silicone oil can be caused by two factors: first, mechanical interaction with the surrounding tissue and, second, the physiochemical properties of the oil itself. The properties of 14 oils of various origins in clinical use were investigated: 12 of the 14 oils contained various amounts of low-molecular-weight components (cyclosiloxanes and molecules with a molecular weight of less than 2,400), which are able to diffuse into the surrounding tissue and may incite toxic or inflammatory reactions. Some of the samples had a ten-fold lower volume resistivity than others, an indicator of the presence of ionic impurities, such as catalyst remnants, which may also be responsible for adverse reactions.