In large bowl, stir together sugar and oil. Add cocoa, blending well. Beat in eggs one at a time, then vanilla.
stir together flour, baking powder, and salt. Add to cocoa mixture. Cover and refrigerate until dough is firm enough to handle, about 6 hours.
Heat oven to 350F. Shape dough into 1 inch balls, roll in powdered sugar. Place about 2 inches apart on cookie sheet. Bake about 12 minutes or until no indentations remains when touched lightly and tops are cracked. Cool.