In a mason jar or bowl, whisk together the oyster sauce, ketchup, soy sauce, and sugar until well combined.
Add the Worcestershire sauce and whisk all together. It's important to taste the sauce and adjust if needed. Keep in mind that you will be using this sauce for the noodles, so the flavor should be strong and not bland. The sauce is now ready to use for the Yakisoba recipe.
You can store the sauce in a mason jar or airtight container for up to a month.