Ken Feinberg said upwards of 100,000 claims that haven't been settled yet simply "lack proof," The Guardian newspaper reported Tuesday.
"The claims that were denied had woeful, inadequate or no documentation to speak of," Feinberg told foreign journalists in Washington Monday.
He did not rule out settling claims at a later date if proper documentation was provided.
Feinberg has been under fire from the Obama administration, U.S. gulf state leaders and local businesses for what they consider to be the slow pace of disbursements from the $20 billion compensation fund.
At the same time, BP has accused Feinberg of being overly generous in his payouts.
Any money remaining in the fund would revert to BP under an agreement with the White House.