Sulfosuccinimidyl oleate (SSO) is a water-soluble, reactive NHS ester derivative of oleic acid used in biochemical and cell biology research. It covalently attaches the oleoyl group to primary amines, such as those on lysine residues of proteins, enabling the study of protein lipidation, fatty acid binding, and lipid-protein interactions. SSO is particularly valuable for labeling cell surface proteins, investigating fatty acid transport proteins (e.g., CD36, FABPs), and as a probe in metabolic studies. Unlike traditional NHS esters, its sulfo group enhances solubility in aqueous buffers, making it suitable for physiological conditions without organic solvents. It is also applied in proteomics to identify lipid-modified proteins and in drug discovery for developing lipid-conjugated molecules.