To reduce or stop the threats to the ecosystems, the local isolate Rhodotorula mucilaginosa S6 was exploited in the analysis of hydrocarbon compounds (both heavy and light crude oil as well as diesel fuel). The results of using Bushnel Haas Medium equipped with 15% hydrocarbon compounds showed a high ability of yeast to decompose and emulsify hydrocarbon compounds in a record time of 10-20 days for both types of crude oil and 7-10 days for biofuel (diesel). The layer of crude oil of both types, heavy, light, and diesel, starting from the fifth day of incubation, as indicated by the change of the color of the entire medium to the dark brown color of oil and honey of diesel, and this indicates the start of the emulsification process, and with the continuation of incubation for 15 days, it was observed that a ring appeared with light bubbles floating on the surface of the nutrient medium. The decomposition outputs using Gas chromatography–mass spectrometry (GC-MS) showed the most important chemical compounds resulting from the decomposition of crude oil. It was found that the heavy crude oil sample treated with yeast suspension consisted of 34 chemical compounds and the light crude oil sample treated in a yeast suspension consisting of 19 compounds, as for biofuels, the results showed that the treatment sample contained 47 compounds, and the compounds appeared at different retention times. The disappearance of some compounds and the appearance of different secondary metabolites in the treatment samples is due to the yeast's ability to analyze them into simple secondary compounds. They can use it as a carbon source of energy.