We developed a high-performance implementation of Gillespie's direct method , with dependency graph and logarithmically scaling sampler optimizations , which we call Reaction Network Monte Carlo (RNMC). RNMC is heavily based on the Stochastic Parallel Particle Kinetic Simulator (SPPARKS) package but with modifications to allow simulating networks with hundreds of millions of reactions and thousands of species. RNMC shares the reaction network and dependency graph between all running simulators and uses a lockless data structure for the dependency graph that allows it to be computed dynamically by all of the simulators in parallel.