The microwave treatment of soils contaminated with heavy- and light-hydrocarbons was investigated. The soils were characterised to determine the total organic liquid content and PAH contents, and the dielectric properties of the soils were measured across a range of temperatures. The heavy- and light-contaminated soils behaved very differently in a microwave environment, with bulk soil temperatures limited to 100 degrees C for the light-contaminated soil. Microwave treatment is shown to remove PAHs from both the heavy- and light-contaminated soils, and it is demonstrated that 95%+ PAH removal can be achieved under moderate processing conditions. Complete remediation of the soils is possible at high microwave powers or long residence times. It is shown that PAH removal can take place at bulk temperatures well below the boiling point of those compounds and a number of explanations are proposed for this behaviour. The mechanisms of PAH removal are investigated for both the heavy- and light-contaminated soils and thermal desorption, selective heating and entrainment mechanisms can all be exploited. This is the first step in the development of a continuous microwave treatment process for the removal of PAHs from contaminated soil on an industrial scale. (C) 2009 Elsevier B.V. All rights reserved,