Trace element levels of heavy metals such as mercury in crude oil are reduced by contacting the crude oil with an oxidant such as oxyhalites, converting elemental mercury into heavy metal cations for subsequent separation from the crude oil. In an improved method for the removal of mercury, at least a complexing agent is added to convert the heavy metal cations into soluble heavy metal complexes in a water phase, which can be separated from the crude oil, for a treated crude oil having reduced levels of heavy metals. In one embodiment, the complexing agent is selected from the group of metal halides.