THE HEAVILY LOADED FUEL TANKER LANDED WITH AN APPROXIMATE 3 KNOT TAILWIND, OVER RAN THE DEPARTURE END OF THE RUNWAY, AND CAME TO A STOP ON A FROZEN RIVER. THE LAST TWO THIRDS OF THE 3,150 FT LONG GRAVEL RUNWAY WAS COVERED WITH ICE. THE CREW STATED THAT THE PROPELLERS EITHER FAILED TO GO INTO REVERSE, OR WERE SLOW IN REVERSING, TO ASSIST IN STOPPING. EXAMINATION REVEALED THAT ALL PROPELLER BLADES WERE IN THE REVERSED POSITION. OUTSIDE AIR TEMPERATURE WAS MINUS 30 TO MINUS 35 DEGREES F. THE AIRPLANE PERFORMANCE CHART USED TO CALCULATE THE LANDING DISTANCE WAS FOR 'CONCRETE RUNWAYS'. STOPPING DISTANCE WAS NOT PREDICATED ON THE USE OF REVERSE PROPELLER THRUST. POST ACCIDENT CALCULATIONS, USING THE SAME CHART, FOUND THE ESTIMATED LANDING DISTANCE NEEDED FOR THE ACCIDENT FLIGHT TO BE 100 TO 200 FT MORE THAN THE LENGTH OF THE RUNWAY.