A gelling agent for viscosifying liquid hydrocarbon fracturing fluids is an aluminum salt of a phosphate ester made by forming the ester by reacting P.sub.2 O.sub.5 with a mixture of organic alcohols which include high molecular weight alcohols or diols selected from hydroxy functional homopolymers, copolymer or terpolymer made from olefins and diolefins selected from the group consisting of ethylene, propylene, butene, butadiene, isoprene, and selected styrenes. The oil based fracturing fluid containing the gelling agent in sufficient concentration to provide a viscosity of between 50 cp and 350 cp at 100.degree. F.