Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13 inch pan.
In a large bowl, combine flour, sugar, cocoa, salt and baking soda. Make a well in the center, and pour in the oil, vinegar, water and vanilla.
Mix well, then pour into a 9x13 inch pan. Bake at 350 degrees F (175 degrees C) for 40 minutes, or until a toothpick inserted into the center comes out clean.