Put the eucalyptus leaves into the crock pot.
Pour oil on top of the leaves. The ratio of herbs to oil should be somewhere around one-quarter of an ounce of eucalyptus to 1 cup of oil. It all depends on how much you want to make.
Turn the crock pot on low heat and let cook for four to eight hours, stirring occasionally with the designated spoon. Any spoon will work for this process, but if you plan on making your own essential oils frequently, then you will want to designate a spoon specifically for this process. Designating a crock pot for this purpose is also a good idea, but not necessary.
Strain the mixture through a cheese cloth and put the strained mixture into the jar.
Seal and store the jar. This is your eucalyptus essential oil, use as desired.