Oxford University Press, like most university presses, is open to direct submissions. It has much better distribution systems than most university presses. They publish nonfiction with an academic focus on a wide range of subjects. They are open to proposals and manuscripts.
Their website is much more thorough in terms of helping outline how the process really works, than most presses. On the page, submitting a proposal, they talk overtly about being open to a wide variety of authors, professionals, and researchers, and it’s clear that they are trying to support that, by really taking the time to make it clear how best one can succeed in terms of creating a compelling and appropriate proposal. They go into details about what they are expecting in terms of a proposal and they also disclose information about the review process.
There are many other helpful pages about the submission process including pages focused on preparing your document, and submitting your manuscript.
In order to submit a manuscript to them, you have to find the appropriate editor to submit to on this page.
They do not disclose royalty rates, and they seem to vary by region.
To learn more or potentially submit, go here.
Emily Harstone is the author of many popular books, including The Authors Publish Guide to Manuscript Submissions, Submit, Publish, Repeat, and The 2022 Guide to Manuscript Publishers.