In a small bowl, thoroughly mix the cornmeal and oil.
Heat the water to boiling; add the salt and pour over the cornmeal. Wait a few minutes, until the cornmeal has absorbed the water and has cooled to lukewarm.
Stir in the flour to form a dough. Turn the dough out onto a lightly floured board.
Wash the bowl and lightly grease it.
Thoroughly knead the dough, lightly sprinkling flour under it only as necessary to keep it from sticking. When it is smooth and resilient, form a ball and place it in the bowl.
Cover with a damp towel and plate, and set it aside for at least 30 minutes, but preferably for several hours or overnight.
Divide the dough into six equal pieces, form balls, and cover them. On a lightly floured surface, roll each ball into a 10-inch circle. Stack the tortillas between waxed paper and cover.
Cook tortillas on a hot griddle for about 20 seconds on each side, until lightly browned but still soft and pliable.