Dietary fish oil supplements are non-FDA regulated health supplements made of fatty oils of fish containing Omega-3 (n-3) polysaturated fatty acids. Pollution of pharmaceutical products, agricultural runoff, and further toxicants into aquatic environments, create a risk of these oils containing lipophilic, bioaccumulative, and persistent organic compounds (POPs), which have been linked to aquatic organisms such as fish. In this study, the top fifteen ranked and consumed dietary fish oil supplements in the 2017 U.S. market were analyzed for identifying small organic molecules such as halogenated POPs and non-halogenated compounds. The analysis was nontargeted by utilizing a novel, comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC/TOF-MS). Sample clean-up was necessary to remove lipids, which was performed by gel-permeation chromatography (GPC) and sulfuric acid digestion. Six halogenated organic compounds (HOCs) were identified across the fifteen samples. Five HOCs were tentatively identified by search similar mass spectra using the NIST mass spectral library, while one HOC was unidentifiable. A mix of 794 unique and isomeric non-halogenated compounds were tentatively identified and 21 of these 794 are frequently occurring across the fish oil supplements. Many of these are naturally occurring, PAH derivatives, and various pesticides. Two isomers of tribrominated diphenylethers (BDE) were separately identified in two fish oil products. BDE-99 was tentatively identified in one fish oil product. According to the product label, the fish oil was previously treated during production to remove contaminants. It is notable, however, that one fish oil product contained three pesticides: chlorpyrifos, malathion, and phosmet. The abundance of HOCs and non-halogenated compounds across the dietary oils were inconsistent with the information given from the bottles: fish ingredients, geographic source of fish used, and treatment processes performed by the companies. Thus, sources of the contaminants in the fish oil dietary supplements are unclear. To prevent consumers’ exposure to contaminants via consumption of fish oil supplements, regulation of fish oil dietary supplements is necessary. An appendix to the thesis, is available for viewing at the Media Center in the SDSU Library.