In oil filtration, particles must attach to the filter medium, typically fibres. Attachment is a function of the chemical and physical properties of both the contaminant and the filter medium. Cellulose and synthetic filter media are commonly used in:oil filtration. The contaminants include wear metal particles, silica and soot. Because of-differences in size and in physical and chemical characteristics, significant differences in contaminant attachment and removal are expected. Experiments were conducted in which filters were challenged with contaminants exhibiting different physical and chemical characteristics. It was found that contaminant shape, roughness and size distribution influence removal. Indirect evidence suggests that chemical interactions also influence removal. The structure of the filter medium mediates these effects.