Search interfaces are mainly designed to support a single searcher at a time. We therefore have a limited understanding of how an interface can support search where more than one searcher concurrently pursues a shared information need. This paper investigated the performance and user behaviour of concurrent search. Based on a recall-oriented search task, a user study was carried out to compare an independent search condition to collaborative search conditions. The results show that the collaborative conditions helped searchers diversify search vocabulary while reducing redundant documents to be bookmarked within teams. However, these effects were found to be insufficient to improve the retrieval effectiveness. We discussed the implications for concurrent search support based on our findings.