A number of bis-(aryl)thiuram disulphides and bis-(aryl)xanthogens have been synthesised and tested as extreme pressure additives using a Seta-Shell four ball lubricant testing machine. Bis-(o-tolyl)thiuram disulphide and bis-(p-sulphonyl)thiuram disulphide are found to be efficient extreme pressure additives showing a higher welding load and a lower scar diameter. Coefficient of friction has been calculated and its variation with load in the case of different additives has been explained. A mechanism for the action of bis-(o-tolyl)thiuram disulphide and bis-(p-sulphonyl)thiuram disulphide with higher weld loads has also been proposed.