In a large bowl, add the water and ripe sourdough starter and whisk until the starter is fully dissolved. Add the sugar and whisk again. In a medium bowl, stir flour and salt together. Add the flour mixture and oil to the starter-water mixture and stir with a spatula until completely combined.
Cover the bowl and let the dough rest for 8 -12 hours, or until the dough nearly doubles.
Lightly grease 2 loaf pans.
Gently turn the dough out onto a lightly floured surface. Shape into a rectangle. Cut the dough in half with a sharp knife and shape each half into a loaf. Place each sourdough loaf into the prepared loaf pans, seam side down. Let the dough rise for about 3 hours or until it is about 1 inch from the rim of the pan.
About an hour before baking, preheat the oven to 425°F.
Once the dough has risen fully, uncover and bake bread for 45 to 55 minutes, or until the crust is golden brown and the internal temperature reaches 204°F.
Remove each loaf from the oven. Turn the loaves out and place them on a cooling rack for at least an hour before slicing.