<p>The data on fluid composition of magma during the formation of dunites of the Guli pluton and olivinites of the Krestovskaya intrusion were obtained by determining the bulk composition of volatile components extracted from melt inclusions in the olivine of the considered rocks using pyrolysis-free gas chromatography-mass spectrometry. The relative concentrations (mol%) of volatile components in the studied mixtures were determined by normalizing the areas of the chromatographic peaks of individual substances to the total area of all peaks. Earlier researches revealed that dunites formed from Na-rich olivine melanephelinite magma. Olivinites formed from K-rich larnite-normative ultramafic magma. These magmas were enriched with hydrocarbons and their oxygenated, sulfonated, and nitrogenated derivatives, CO₂, and H₂O. The total amount of hydrocarbons is 69.39&#xa0;mol% and 59.61&#xa0;mol% in melanephelinite magma and larnite-normative ultramafic magma, respectively. Among hydrocarbons oxygenated compounds prevail: 62&#xa0;mol% in melanephelinite magma and 52.17&#xa0;mol% in larnite-normative magma. The amount of sulfonated and nitrogenated compounds and CO₂ in melanephelinite magma is 13.2&#xa0;mol%, 8.1&#xa0;mol%, and 0.95&#xa0;mol%, respectively, which is 2–3 times higher compared to that in larnite-normative ultramafic magma. The water content reaches 8.40&#xa0;mol% in melanephelinite magma and 31.17&#xa0;mol% in larnite-normative ultramafic magma. The irregular ratios of volatile components in these magmas indicate their significant difference and crystallization of dunites and olivinites from different parental magmas. A comparison of the obtained data with those in diamonds from kimberlite pipes in Yakutia and placer deposits of the northeastern Siberian Craton and the Urals suggests that the generation of magmas responsible for the formation of the studied rocks occurred under reducing conditions in the upper mantle with abiogenic hydrocarbon present.</p>