Mercury is one of most dangerous contaminants of natural gas and petroleum and petroleum fractions present in the crude oil industry due to its corrosive properties. The determination of Hg levels in petroleum products is a prerequisite for risk evaluation and ensuring an efficient Hg removal. This Review focuses on total and speciation analyses of Hg in the petroleum industry. We describe the constraints related to sampling and analysis for both natural gas and liquid petroleum products and the different methodologies developed over the past decades. Despite the low detection limits reached with various methodologies, the reliability of measurements might strongly depend on sampling and storage practices. The preservation of all Hg species from sampling to analysis might require some further evaluation. We evaluated the speciation methodologies based on reported performances. We however conclude that the lack of reference material for Hg speciation analysis in petroleum hampers a robust evaluation of the methods. Future developments might allow a better characterization of the different Hg species, helpful to understand the partitioning of Hg between the different petroleum phases.