For the purpose of determining under section 10(1)(b) what oil is to be disregarded in computing a participator's gross profit or loss attributable to oil won from the field after the transfer there shall be treated as if it were the new participator's, and not the old participator's, the whole or, if the transfer is of part of the old participator's interest in the field, a corresponding part of the old participator's share of oil won and saved from the field before the transfer.