Provided are a computer program product, system, and method for modifying a series of lock acquire and release operations to use a single lock reservation. A representation of source code is scanned to determine a series of acquire lock program statement and release lock program statement pairs to acquire and release a lock by a thread. A first acquire lock program statement in the series is modified to be an acquire with reserve program statement that when executed by the thread causes the thread to acquire the lock and indicate the lock as reserved for use by the thread. A last release lock program statement in the series is modified to be a release with cancel program statement that when executed by the thread causes the thread to release the lock and indicate the lock as not reserved.