Celery and Parsley are very similar in regard to their variation in oil content.
Here is some info on the different parsley strains with their oil constituents.
Main constituents
There are three cultivated varieties, which in part differ by their chemisms. Var. latifolium (broad-leaved) and var. crispum (curly-leaved) are grown for their leaves, and var. tuberosum is grown for its root.
The essential oils of leaves and root show approximately the same composition. The main components (10-30%) are myristicin, limonene and 1,3,8-p-menthatriene; minor components are mono- and sesquiterpenes. The curly varieties (var. crispum) tend to be richer in myristicin, but contain much less essential oil than var. latifolium (0.01 and 0.04%, respectively).
In contrast, the essential oil from the fruits (3-6%) is either dominated by myristicin (60 to 80%; mostly var. tuberosum and var. crispum) or by apiole (70%; mostly var. latifolium). A third chemical race shows allyl tetramethoxy benzene (55 to 75%), which can also appear in apiol-dominated oils (up to 20%).