A surface active agent characterized as an ethoxylated or propoxylated ester, or ester constituted of a 1,4 sorbitan skeleton to which at least one and up to three ethoxy, propoxy, or mixed ethoxy-propoxy substitutent, and at least one fatty acid substitutent is attached through oxygen to the 2,3,5 and 6 carbon atoms. The surfactant is useful for removing very finely divided particulate solids from unconventional whole heavy petroleum crudes, heavy petroleum crude fractions, and residua, syncrudes and syncrude fractions, particularly shale oil and shale oil fractions, by the use of novel surface active agents.