The radio jets associated with NGC 6251, NGC 315, and 3C 31 are subjected to hydrodynamic detachment criteria in the ultrarelativistic and nonrelativistic limits under the assumption of the steady laminar motion of a perfect gas. All the jets demonstrate allowable sonic heights. However, all except the south jet in 3C 31 detach before the shoulder in their transverse intensity profiles. It is concluded that the observed spreading of these jets cannot be due simply to the action of a decreasing background pressure on a laminar jet boundary in steady motion. 12 references.