  Given a graph $G = (V, E)$, a set $S \subseteq V \cup E$ of vertices and
edges is called a mixed dominating set if every vertex and edge that is not
included in $S$ happens to be adjacent or incident to a member of $S$. The
mixed domination number $\gamma_{md}(G)$ of the graph is the size of the
smallest mixed dominating set of $G$. We present an explicit method for
constructing optimal mixed dominating sets in Petersen graphs $P(n, k)$ for $k
\in \{1, 2\}$. Our method also provides a new upper bound for other Petersen
graphs.
