  The purpose of quantization for a probability distribution is to estimate the
probability by a discrete probability with finite support. In this paper, a
nonuniform probability measure $P$ on $\mathbb R^2$ which has support the
Sierpi\'nski carpet generated by a set of four contractive similarity mappings
with equal similarity ratios has been considered. For this probability measure,
the optimal sets of $n$-means and the $n$th quantization errors are
investigated for all $n\geq 2$.
