reversible gels formed from flexible polymers e g polystyrene these gels form in hydrocarbon solvents and it is possible to promote gel formation e g at different concentrations and at different temperatures the variables of molecular weight and polymer side chain structure are seen to control thermally reversible gel formation in this system and these variables are readily controlled in these polymers the ability to create thermally reversible gels in hydrocarbon solvents or in particular liquid hydrocarbon fuels provides an extremely effective method for controlling the physical character of hydrocarbon fuels along with extraordinary implications with respect to their ability to restrict the damaging effects of such fuels in a given crisis situation for example hydrocarbons can now be converted into a much less dangerous form a gel which would minimize their ability to spread if upon accident they were to escape from a containment vehicle however upon appropriate selection of temperature as disclosed herein i e by thermally reversing the gel in general by temperature change or by depolymerization e g of the polyisocyanate to trimer structure these gels can be reconverted back to a free flowing fluid and be delivered in the manner made necessary by a particular combustion mechanism furthermore when large quantities of hydrocarbons are shipped the risk of environmental contamination can now be minimized as gels can now be rationally developed for such hydrocarbons on a predictable basis and accordingly such gels would not release as quickly into the environment in the event of leakage or the complete rupture of a storage tank when in transport the implication of minimizing or even eliminating the risks involved in petroleum shipment transport for example is extraordinary those skilled in the art will recognize or be able to recognize by no more than routine experimentation many.