From the Horror Tree website:
Thank you for your interest and for thinking of 13Horror.com as a potential home for your terrifying short story!
We are currently accepting submissions for our third short horror story anthology, Thirteen Volume Three. This will be published later this year as a paperback book and as an e-book. Our previous two anthologies, Thirteen Volumes One & Two, have topped the iTunes Horror Charts in America, Canada, the United Kingdom and Australia, and we intend for Volume Three to do the same.
Before you submit your story, please read the Theme and Formatting Guidelines and the Terms and Conditions sections below. These are important so that you are happy 13Horror is the right place for you to submit your story and for you to understand what publication with us will mean for you. You will also need to complete the Submission Form and send it, along with your story, to [email protected] The Submission Form is available on the 13Horror.com website.
Further details can be obtained at http://horrortree.com/taking-submissions-thirteen-volume-three/