If you don't want to take anybody's word for it, you can calculate a fairly reasonable estimate yourself.
Let Numerator = Max Open Interest on any one day
Let Denominator = Sum of Volume of all trading days
Then (Numerator / Denominator) is a fairly decent approximation of the percent of contracts that are delivered. This estimate will be an "upper bound", i.e., it will be equal to, or greater than, the correct value. (It's an upper bound because it assumes that the number of contracts delivered against, is equal to the max open interest throughout the lifetime of the contract).
I just did this little calculation myself for the March 2008 contract of Crude Oil and got this result: approx 3.88% OR LESS of the traded contracts of March 2008, were delivered against. See attached Excel spreadsheet.
Let Numerator = Max Open Interest on any one day
Let Denominator = Sum of Volume of all trading days
Then (Numerator / Denominator) is a fairly decent approximation of the percent of contracts that are delivered. This estimate will be an "upper bound", i.e., it will be equal to, or greater than, the correct value. (It's an upper bound because it assumes that the number of contracts delivered against, is equal to the max open interest throughout the lifetime of the contract).
I just did this little calculation myself for the March 2008 contract of Crude Oil and got this result: approx 3.88% OR LESS of the traded contracts of March 2008, were delivered against. See attached Excel spreadsheet.