A Business Process (BP) consists of some business activities undertaken by one or more organizations in pursuit of some business goal. Tools for querying and analyzing BP specifications are extremely valuable for companies as they allow to optimize the BP, identify potential problems, and reduce operational costs. In particular, given a BP specification, identifying the top-k execution flows that are most likely to occur in practice out of those satisfying the query criteria, is crucial for various applications. To address this need, we introduce in this paper the notion of likelihood for BP execution flows, and study top-k query evaluation (finding the k most likely matches) for queries over BP specifications. We analyze the complexity of query evaluation in this context and present novel algorithms for computing topk query results. To our knowledge, this is the first paper that studies such top-k query evaluation for BP specifications.