Fluid inclusion studies were conducted in the vein quartz known as the "Marmarosh diamonds" of the Krosno and Dukla zones of the Ukrainian Carpathians, which are potentially oil- and gas-bearing. The "Marmarosh diamonds" contain different types of fluid inclusions which record the evolution of the quartz formation. The inclusions were studied by means of gas chromatography, microthermometry and fluorescence. The following sequence has been observed: methane inclusions displaying characteristic features due to crystallography, light hydrocarbons, complex inclusions with a variety of bitumens, and gas-liquid inclusions with two different hydrocarbon phases. The regions where the light hydrocarbon inclusions occur seem to be the most promising as regards oil and gas prospects.