The following Nerf Bars were designed to fit your Mercury Mariner:
Go Rhino 4000 Series Nerf Bars- $191.95
Steelcraft 3" Round Step Nerf Bars- $169.95
Westin Signature Series Nerf Bars- $217.95
Model years for Mariner nerf bars include 2009, 2008, 2007, 2006, 2005, 2004, 2003, 2002, 2001, 2000, 1999 and earlier.