Cumulative plasma jets formed by hollow cones imploded via laser ablation of their outer surfaces were observed. The velocity, shape, and density of the jets are measured with monochromatic 0.65keV x-ray imaging. Depending on cone geometry, cumulative jets with ion density ∼2×1020cm−3 and propagation velocities >10km∕s are formed. Similar results are observed when jets are formed by imploding wedges. Such jets can be used to simulate hydrodynamics of astrophysical jets interacting with stellar or interstellar matter.