Mercury contamination from gas and condensate can cause concerns in the safe operation of LNG plants, LPG plants and naphtha crackers. The mercury contamination is tenacious and it is difficult to decontaminate the systems by clean gas or condensate purging. We have demonstrated in the laboratory that the systems contaminated with mercury, both from gas and liquids condensate, can be passivated effectively. The most effective passivation procedure is to discontinue the normal processing, remove the hydrocarbon from the system, inject HIS gas into the system for adsorption and then how with air, both at atmospheric pressure and room temperature. Because of its effectiveness, simplicity, and mild conditions, this process lends itself to field applications in the plants and storage tanks. The process could be implemented safely by handling H2S carefully, injecting H2S slowly and stopping H2S injection as soon as the H2S could be detected at the exit of the systemThe procedure involves three chemical steps. The H2S is adsorbed on the Hg and then reacts with O-2 to form nascent sulfur [S]. Finally, [S] reacts with Hg to form innocuous HgS. This procedure appears to be effective for all types of Hg compounds, including the organic mercury in the condensate.