Numerous geological and geological–geochemical studies have shown that water, in particular, heated and overheated aqueous solutions, plays an active role in the formation and migration of hydrocarbons in the Earth’s interior [3, 5, 6]. At the same time, the behav� ior of hydrocarbons in aqueous solutions, their phase states, and transformations, especially under high and ultrahigh temperature–pressure conditions, have not yet been established conclusively and require special experiments. Research based on visualization of pro� cesses in fluid inclusions in synthetic minerals that were formed simultaneously with realization of aque� ous–hydrocarbon interaction are the most promising in this respect. The study of these inclusions by opti� cal, fluorescent, and luminescent microscopy, local IR spectroscopy, and microthermometry makes it possible not only to determine the composition and aggregate state of the parental medium, but also to observe in situ the behavior and transformations of