Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13 inch pan.
In a large bowl, stir together the cocoa and baking soda. Add 1/3 cup vegetable oil and boiling water. Mix until well blended and thickened. Stir in the sugar, eggs, and remaining 1/3 cup oil. Finally, add the flour, vanilla and salt; mix just until all of the flour is absorbed. Spread evenly into the prepared pan.
Bake in the preheated oven for 35 to 40 minutes, or until a toothpick inserted into the cake comes out clean. Allow to cool before cutting into squares.