Scour data were collected during 1936-94 at 22 bridge sites in Mississippi. The drainage area of the bridge-scour sites ranged from 60.8 to 5,720 square miles, and the slope in the vicinity of each site ranged from 0.00011 to 0.00163 foot per foot. Measured pier-scour depths ranged from 0.6 to 20.4 feet. Measured total-scour depths at minimum-bed elevation ranged from 5.2 to 29.8 feet. Recurrence intervals of measured streamflow discharges ranged from less than 2 years to about 500 years. All of the Mississippi pier-scour depths were within 2.3 times the normal pier width, which agreed with previous research. Only 12 (6 percent) of the 190 measured pier-scour depths were greater than 1.1 times the normal pier width. Measured pier-scour depths were as much as 2.24 times a normal pier width of 3.3 feet. However, for pier widths greater than about 4 feet, measured pier-scour depths were significantly less than 2.3 times the normal pier width. An envelope-curve equation for the Mississippi pier-scour data was developed by relating pier-scour depth divided by normal pier width to measured approach-flow depth divided by normal pier width. The envelope-curve equation predictions could be used for reasonable verifi- cations of the HEC-18 pier-scour predictions, currently required for the design and mainte- nance of bridges over waterways in Mississippi.