Lightly grease 9x13 baking pan, and preheat oven to 325 degrees,
Mix sugar, butter and oil in a bowl, and add eggs one a a time.
Slowly incorporate sifted flour and cocoa, and mix until blended.
Add vanilla and salt and mix.
Stir in pecans, and pour into pan.
Bake at 325 degrees for 30-35 minutes until toothpick inserted in center comes out clean.
Remove from oven and cover evenly with marshmallows.
Return to oven for 2-3 minutes, and remove. Immediately pour icing on top, and let set for at least 30 minutes.