In a large bowl, dissolve yeast in warm water. Add the oil, sugar, salt, eggs and 4 cups flour. Beat until smooth. Stir in enough remaining flour to form a firm dough. Turn onto a floured surface; knead until smooth and elastic, 6-8 minutes. Place in a greased bowl, turning once to grease top. Cover and let rise in a warm place until doubled, about 1 hour.
Punch dough down. Turn onto a lightly floured surface; divide in half. Divide each portion into thirds. Shape each piece into a 15-in. rope.
Place three ropes on a greased baking sheet and braid; pinch ends to seal and tuck under. Repeat with remaining dough. Cover and let rise until doubled, about 1 hour.
Beat egg and cold water; brush over braids. Sprinkle with sesame or poppy seeds if desired. Bake at 350° until golden brown, 30-40 minutes. Remove to wire racks to cool.