  We study mass conservation errors (momentum density spike) and the related
phenomenon of post shock oscillations in numerical solutions of compressible
Euler equations. These phenomena and their causes have been reported in
literature [34, 1]. In this paper, first, we compare the mass conservation and
post shock oscillation errors obtained using combinations of different
numerical methods (Finite Volume, Finite Difference with WENO and DG with
simple WENO limiter) and upwind flux functions (ROE, AUSM+-up, and others) for
moving shocks, modelled using one-dimensional Euler equations. Next, the mass
conservation error is quantified for stationary shocks modelled using
one-dimensional, quasi-one-dimensional and two-dimensional Euler equations. It
is shown that using a fine mesh or refining mesh near shocks using multiple
over set meshes lead to mitigation of the mass conservation error. This is
demonstrated using the problem of flow through a variable area duct modelled
using quasi-one-dimensional Euler equations. The link between mass conservation
error and carbuncle formation is shown and preliminary results indicating that
the carbuncle can be cured using multiple overset meshes are also shown.
