I know that they share code, and that the Oracle Java team commits to the OpenJDK code. If they're actually the same right now, idk, bit it's often been the case that they aren't. It's often been the case that the OpenJDK JRE and the Oracle JRE have different performance characteristics. Oracle JRE 8-10 bundled JavaFX, while there was no JavaFX for OpenJDK (in JRE 11 Oracle open-source JavaFX as OpenJFX).