Fat-and-oil products (margarine and spreads) are included in the daily diet and meet the requirements for“wholesome foods”. It is a substitute for butter used in cooking. The purpose of a series of studies regardingthe fat phase of margarine and spreads was to determine the amounts of fatty acids and their isomers withthe highest possible degree of detail in fat-and-oil products, as well as to improve the methodology using gaschromatographic methods in combination with mass spectrometry. 17 samples of fat-and-oil products wereused for analysis and comparison in this study. All measurements were performed using a triple quadrupoleGC-MS/MS Thermo Scientific™ TSQ 8000™ system equipped with GC Thermo Scientific™ TRACE™1310 with SSL Instant Connect™ SSL module and Thermo Scientific™ TriPlus™ RSH autosampler. Thearticle shows the possibility of using information about fatty acid composition to establish the species offat-and-oil products. The study presents the fatty acid composition of margarine and spreads. It is shownthat the high-resolution mass spectrometry method for inferring the fatty acid composition is very useful foridentifying things that come from plants and animals.