In a large mixing bowl, dissolve sugar in warm water. Sprinkle yeast over the top and let sit for 10 minutes until frothy.
Whisk in oil, then beat in the eggs one at a time. Add salt and gradually add flour, mixing until the dough comes together.
Knead the dough on a floured surface for about 10 minutes until smooth and elastic. Place in a greased bowl, cover, and let rise in a warm place for 1-2 hours until doubled in size.
Preheat oven to 375°F (190°C). Punch down the dough and divide into 3 equal pieces. Roll each piece into a long rope and braid them together.
Place the braided loaf on a parchment-lined baking sheet. Beat the egg yolk with 1 tablespoon of water and brush over the loaf.
Bake for 30-35 minutes until golden brown and sounds hollow when tapped on the bottom. Let cool on a wire rack before slicing.