Getting Tiles...what projection are they in?

I have a desktop GIS application. I am going to retrieve tiles from OSM and displaly them in my application. This will be one of many layers of GIS data in the view. How can I find out what projection the tiles given from OSM are in?

I can get tiles based on extents of view, I can get the extents of each tile, but I need to know what projection they are in, specifically EPSG.

thx,

Todd P

EPSG 3785. http://docs.openlayers.org/library/spherical_mercator.html