Brown and black mustard are two valuable species used as raw materials in the agro-industrial sector, particularly for their aromatic, medicinal, and potential bioenergy applications. This study aimed to evaluate the crude oil and essential oil contents and chemical compositions of six domestic mustard lines (three brown and three black mustard) cultivated in Türkiye. Fatty acid profiles of crude oils were analyzed using gas chromatography (GC), while essential oil components were determined via gas chromatography-mass spectrometry (GC-MS). Significant variability (p<0.01) was observed among the lines for both essential oil and fatty acid composition. Among essential oil components, allyl isothiocyanate was the major compound across all lines, ranging from 69.44% in the Tekirdağ brown mustard line (J1) to 97.56% in the Türkiye-1 black mustard line (N1). Other prominent constituents included 2-butenenitrile (0.93-1.93%), 3-butenyl isothiocyanate (0.20-2.22%), and, to a lesser extent, propyl isothiocyanate, 2-hexanol, and beta-phenyl ethyl isothiocyanate in specific lines. The maximum essential oil content (1.02%) was obtained from the Ankara black mustard line (N2), while the minimum (0.20%) was recorded in the İzmir brown mustard line (J2). Fatty acid analysis showed that erucic acid (C22:1) was the predominant fatty acid in black mustard lines (38.43-38.92%) compared to brown mustard lines (20.94-23.16%). In contrast, oleic acid (C18:1) content was higher in brown mustard-reaching up to 24.81% in the J2 than in black mustard lines (13.08-13.65%). Linoleic acid (C18:2) ranged from 15.01% to 22.01% across all lines. The highest crude oil content was observed in the J2 at 34.86%, whereas the lowest was found in the N1 at 27.19%. These results highlight the significant chemical diversity among domestic mustard lines in Türkiye and demonstrate their potential for use in breeding programs targeting industrial oil production and functional bioactive compounds.