The present invention relates to novel oligomers of the formula R.sub.f --E--S--M.sub.1 ].sub.x [M.sub.2 ].sub.y H, and mixutes thereof, wherein R.sub.f is a perfluoroalkyl group, E is a linkage group, --M.sub.1 -- represents a hydrophilic monomer unit, --M.sub.2 -- represents a hydrophobic monomer unit, x and y represent the number of monomer units present in the novel oligomers. The sum of x and y is between 4 and 500 and x/(x+y) is between 1 and 0.5. The novel oligomers are useful as additives in protein foam type fire fighting compositions improving foam expansion, foam drainage and extinguishing times and reducing flammability of hydrocarbon contaminated protein foams. The novel oligomers are further useful as surface tension depressants providing improved wetting, spreading and leveling properties in aqueous systems.