Heat oil in a saucepan or deep-fryer to 375 degrees F (190 degrees C).
Pour buttermilk into a medium bowl. In a separate bowl, stir together the flour, salt, pepper and oregano. Dip squid rings into the buttermilk, then into the seasoned flour.
Place the coated pieces in the hot oil, and fry in small batches, turning if necessary, for even cooking. When evenly browned, remove to paper towels to drain, and continue with the rest of the squid. Serve hot.