Compositions for treating high-molecular-weight components of a petroleum fluid are generally disclosed. In some embodiments, such compositions include olefinic ester compounds, such as alkyl esters of C10-18 unsaturated fatty acids. In some embodiments, such compositions are added to a petroleum fluid to improve the rheological properties, e.g., breaking up or inhibiting the precipitation of high-molecular-weight components of petroleum fluids. In some other embodiments, such compositions are used for removing deposits of such high-molecular-weight components from the surfaces of equipment used for extracting or transporting petroleum or natural gas.