Sterilize your jars and lids. Once your ketchup has reduced, pour into the jars and put on the lids. Fill the jars to about 1/2 inch from the top and make sure to wipe the rims clean before you put on the lids.
Process the jars of ketchup in a hot water bath for about 15 minutes (bring to a boil and boil for 15 min). Make sure the water covers your jars by at least 1/2 inch.
Once the jars have sealed (you will hear the lids pop), label your jars and you are done!