  We prove the following characterization of the weak expectation property for
operator systems in terms of Wittstock's matricial Riesz separation property:
an operator system $S$ satisfies the weak expectation property if and only if
$M_{q}(S)$ satisfies the matricial Riesz separation property for every $q\in
\mathbb{N}$. This can be seen as the noncommutative analog of the
characterization of simplex spaces among function systems in terms of the
classical Riesz separation property.
