Under 1970 technology ... the average refinery cracked around 19 gallons of gasoline and 12 gallons of diesel, or heating oil. The remainder of the forty-two gallons (11 gallons) does not all go to waste. Close to ten gallons, or it's equivalent, is used for the manufacture of other petroleum based products.

From what I was told, out of the forty-two gallons of crude ... less than two gallons go to waste ..

Again, that's 1970 stuff. I really don't know what today's technology has improved that old mix.