The Java Astrodynamics Toolkit (JAT) is an open source software library of reusable software components for mission design, trajectory optimization, and simulation of navigation, guidance and control systems. This paper provides results of comparing various Earth orbit ephemerides created with JAT with those created using Analytical Graphics Inc.'s Satellite Tool Kit/High Precision Orbit Propagator (STK/HPOP) and a.i. solutions, Inc.'s FreeFlyer. Ephemerides produced using STK and FreeFlyer are also compared to each other. With careful attention to parameters and models, results show agreement of millimeter to meter level over several days. Differences are discussed including potential sources of error.