Jet swelling is shown to exist when a concentrated oil-in-water emulsi
on is ejected from a capillary tube into a stagnant fluid. The jet swe
lls up to ten times the diameter of the capillary tube depending on th
e shear rate in the tube and the density difference between the ejecte
d and the stagnant fluid. The relative jet swelling increases with sil
icone oil concentration, decreases in silicone oil viscosity, decrease
s in tube diameter, and decreases in tube length. The diameter ratio (
jet/tube) grows as the 1/3 power of the wall shear stress in the capil
lary tube. The analogy between the swelling behavior of these emulsion
s and that observed in dilute and semidilute polymer solutions is disc
ussed.