Metal cross-linked phosphate ester compositions impart fragile progressive gel structure to a variety of oil and invert emulsion-based drilling fluids at neutral or acidic pH. The fluids are useful for drilling wellbores in subterranean formations without need for organophilic clays to suspend drill solids. At greater concentrations, metal cross-linked phosphate ester compositions enhance fluid viscosity for suspending weighting materials in drilling fluids during transport of the fluids, as from a manufacturing or mixing facility to a drilling site.