  Using the conservation of energy and momentum during collisions of any two
shells, we consider the efficiency of gamma-ray bursts by assuming that the
ejecta from the central engine are equally massive and have the same Lorentz
factors. We calculate the efficiency and the final Lorentz factor of the merged
whole shell for different initial diversities of Lorentz factors and for
different microscopic radiative efficiency. As a result, a common high
efficiency in the range of 0.1 to 0.9 is considerable, and a very high value
near 100% is also reachable if the diversity of the Lorentz factors is large
enough.
