Collocational prepositional phrases like ten koste van (at the expense of), met het oog op (with an eye on), and onder het mom van (under the pretext of) are patterns of the form P-NP-P, which have a non-compositional semantics and which are syntactically rigid or idiosyncratic. We present a number of linguistic tests which set such items apart from regularly built prepositional phrases. To find candidate strings which should be included in a computational lexicon as collocational prepositional phrases, we extract all instances of the relevant pattern from a corpus annotated with POS tags. Next, we introduce a number of statistical tests (mutual information, log-likelihood, and