This study demonstrates that oil-contaminated drill cuttings (OCDC) from North Sea platforms can be treated in a single-mode microwave cavity such that the residual oil levels can be reduced to below the current environmental discharge limits. A number of process parameters have been investigated, including microwave power, treatment time, sample mass, and moisture content. Although the discharge limits were not achieved in a number of cases, it is shown that enhancing the concentration of dielectric heaters or multistage processing are strategies which result in residual oil levels which are well below the environmental limit. For a sample mass of 100 g, it is shown that treatment times as low as 3 s can be sufficient to remove the required amount of oil; this is much faster than equivalent tests in multimode cavities.