  We calculate merger rates of dark matter haloes using the Extended
Press-Schechter approximation (EPS) for the Spherical Collapse (SC) and the
Ellipsoidal Collapse (EC) models.
  Merger rates have been calculated for masses in the range
$10^{10}M_{\odot}\mathrm{h}^{-1}$ to $10^{14}M_{\odot}\mathrm{h}^{-1}$ and for
redshifts $z$ in the range 0 to 3 and they have been compared with merger rates
that have been proposed by other authors as fits to the results of N-body
simulations. The detailed comparison presented here shows that the agreement
between the analytical models and N-body simulations depends crucially on the
mass of the descendant halo. For some range of masses and redshifts either SC
or EC models approximate satisfactory the results of N-body simulations but for
other cases both models are less satisfactory or even bad approximations. We
showed, by studying the parameters of the problem that a disagreement --if it
appears-- does not depend on the values of the parameters but on the kind of
the particular solution used for the distribution of progenitors or on the
nature of EPS methods.
  Further studies could help to improve our understanding about the physical
processes during the formation of dark matter haloes.
