Concurrency control on B+ trees is primarily achieved with latches, but serialization and contention can hinder scalability. As core counts on current processors increase, it is imperative to develop scalable latch-free techniques for concurrency control. The authors present PALM, a novel technique for performing multiple concurrent queries on in-memory B+ trees. PALM is based on the Bulk Synchronous Parallel model, which guarantees freedom from deadlocks and race conditions. Input queries are grouped and processed in atomic batches, and work proceeds in stages that preclude contention.