The extracellular glycolipids produced by the yeast, Rhodotorula bogoriensis ( formerly Candida bogoriensis), were analyzed using an LC/API-MS method. The analysis confirmed that the predominant form the sophorolipid structure contained a C22 hydroxy carboxylic acid. A minor amount (< 10%) of a C24 hydroxy carboxylic acid in the sophorolipid was also found, which had not been reported previously. The sophorolipid product, which contained varying degrees of acetylation at the primary hydroxy groups of the sophorose sugar, was deacetylated with sodium methoxide. The des-acetylated sophorolipid was esterified using an immobilized lipase as catalyst in tetrahydrofuran and the product analyzed by mass spectrometric techniques. The product was screened for dimer or polymer formation but only a monomeric lactonized sophorolipid structure was detected.