Product review (5 stars): My oven does not have a flat bottom.
My new oven bottom is not flat - it has a 2 inch border then drops down in the center.  I was able to place the liner on the border and it stays in place.  It will catch drips but if anything heavy spills, the liner will bow and possibly spill into the oven.  Not the liner's fault - just my oven.  I didn't realize my oven was not flat until I purchased these liners.