While a clear distinction is established between simple lookup tasks and complex exploratory tasks, few studies have documented the differences between complex lookup tasks and simple exploratory tasks. To address this empirical gap, which has implications for system adaptability, the present study focused on these differences and the impact of users’ prior domain knowledge (low vs. high) on exploration-exploitation search strategies (thematic and navigational). The effects of prior domain knowledge on information search performance were also investigated, as well as the extent to which the navigational and thematic search strategies predicted users’ search scores and learning outcomes. Sixty students (35 in psychology, 25 in computer science) were asked to perform two complex lookup tasks and two simple exploratory tasks within and outside their knowledge domain. Results showed that when users performed tasks in their knowledge domain, they formulated more specific queries, achieved higher search scores, and produced higher quality factual knowledge. Complex lookup tasks led to more thematic exploitation and more navigational exploration than simple exploratory tasks. The search strategies predicted output performances differently, depending on the search domain (in vs. out). In light of these results, solutions helping users to improve their search strategies are given.