Chemically Talking, this molecule is "halfway" in between Sorbitan Oleate and Sorbitan Trioleate, that means that it is also an attachment of sorbitan (a dehydrated sorbitol (sugar) molecule) with the unsaturated fatty acid Oleic Acid, but in a very ratio of two:3 as a result the "Sesqui" element within the molecule's title. Other than having a go