An average is fine, and ideally specific to the bitter orange tree. I'm trying to understand the economics of cultivating for Neroli oil.
I've got a proper answer in a book called "The Complete Technology Book of Essential Oils" by the NIIR Board. Paraphrasing:
You get about 6kg per tree per year for a 10-year old tree Older trees, about 20kg. Average: 5-10kgs (Southern France).