Mass-transfer coefficients between solid surfaces and submerged or unsubmerged liquid multijets are measured electrochemically. Various types of distributors are used; the open area Af ranging from less than 5 to more than 97%. Unsubmerged and submerged multijets perform differently at high values of Af when the injection Reynolds number is smaller than approximately 2000; the unsubmerged multijets interact with each other, thus forming a particular single jet which performs better than the corresponding submerged multijets.