How are books chosen for Overdrive?

[passero]

Hi! I couldn't figure out where to put my question so I hope this is okay.

I was wondering if anyone knows how libraries select books to offer on Overdrive. Do they get to choose each book and format individually, or do they just choose from packages?

I was just wondering if it would be worthwhile to request certain books and formats. My library offers most of the books I want, but only as audio books. The ebooks they have are mostly reference or self-help books, and mostly PDFs. They do have *one* epub in their collection. If I ask them for a certain book in epub, is it likely that they could get it for me?