Compositions comprising at least one C4-C30 olefin or oxidation product thereof and kerosene or an aromatic solvent are particularly effective for use in removing asphaltene and asphaltene-containing organic deposits and in preventing or reducing the precipitation and deposition of asphaltenes from hydrocarbon fluids. When added to heavy oils comprising asphaltenes, alone or in combination with dispersants and further inhibitors, the invented compositions lower viscosity and pour point, and aid in preventing asphaltene precipitation during transport and in combustion.