Exposure to mercury and its compounds poses a potential health risk to workers involved with inspection and maintenance activities in facilities that process hydrocarbons containing significant amounts. The risks of exposure to mercury are often underestimated for a variety of reasons. Foremost is the fact that the exact amount of mercury present in processed petroleum often is not known with certainty. Secondly, the specific quantities of mercury compounds that may be present in hydrocarbon liquids seldom are known at all. Thirdly, monitoring for mercury vapor in work environments is not a routine procedure for many processing facilities. Lastly, mercury toxicity is gradual and produces no immediately apparent impairment that can easily be associated with occupational exposure. Superimposed on the risk issues are several aspects of the chemistry of mercury that make it illusive both to quantitative analysis and to detection in work environments. Tbe combination of the cited factors increases the likelihood that workers who are inadvertently exposed to occupational environments that contain mercury will be adversely affected.