Prolonged room temperature stability (i.e. zero particle growth) can be achieved for concentrated emulsions of perflubron (perfluorooctyl bromide) or perfluorodecalin via addition of a secondary high molecular weight, lipophilic fluorocarbon component. Due to their enhanced lipophilic character, the secondary fluorocarbon components have acceptable half-lives in the organs of the reticuloendothelial system.