  New two- and three-dimensional calculations are presented of relativistic jet
propagation and break out in massive Wolf-Rayet stars. Such jets are thought
responsible for gamma-ray bursts. As it erupts, the jet is surrounded by a
cocoon of less energetic, but still highly relativistic ejecta that expands and
becomes visible at much larger polar angles. These less energetic ejecta may be
the origin of X-ray flashes and other high-energy transients which will be
visible to a larger fraction of the sky, albeit to a shorter distance than
common gamma-ray bursts. Jet stability is also examined in three-dimensional
calculations. If the jet changes angle by more than three degrees in several
seconds, it will dissipate, producing a broad beam with inadequate Lorentz
factor to make a common gamma-ray burst.
