The Social Security Administration improperly awarded disability benefits in more than 25 percent of cases examined between 2006 and 2010, according to a new Senate report -- potentially costing taxpayers millions of dollars.

The findings conclude an 18-month investigation by the chamber’s Permanent Subcommittee on Investigations and show that roughly a quarter of the 300 randomly selected disability cases were awarded benefits “without properly addressing insufficient, contradictory and incomplete evidence.”

Each questionable decision can mean a big taxpayer expense. According to one estimate, the average lifetime disability award is $300,000.

The investigation was led by Oklahoma Sen. Tom Coburn, a medical doctor and the subcommittee’s top Republican. He said the bipartisan report shows information gathered over the past several years concludes the Social Security Disability Insurance and Supplemental Security Income programs are “teetering on financial bankruptcy.”

The 136-page report focuses on questionable benefits rulings made by administrative law judges, including one in Oklahoma who was found to have awarded more than $1.6 billion in lifetime benefits in just three years. Judge Howard O’Bryan, in Oklahoma City, approved roughly 90 percent of more than 5,400 cases from 2007 to 2009 -- most of them held “on-the-record” without hearings, according to the minority report.

The report also found the agency since January 2009 added 5.9 million Americans to the disability rolls. And in 2011, 10.6 million people were receiving more $128.billion in disability insurance payments, the report said.

“The question is: Are benefits going only to those who are supposed to be getting to them?” Coburn asked Thursday during a Capitol Hill hearing on the issue. “The purpose of this program is to make sure that all Americans have a safety net if they become disabled and can no longer work. It should be remembered though that this law means ‘being unable to work any job in the national economy.’ ”

The Social Security Administration responded Monday, acknowledging the concerns and vowing continued improvement.

"We share the subcommittee’s concern that a small number of judges have failed our expectations with regard to a balanced application of the law, proper documentation, proper hearings and proper judicial conduct,” agency spokesman Mark Hinkle said.

He said the agency has undertaken a “vigorous set” of initiatives since the time most of the cases were decided, about five years ago, and has made substantial progress.

“We recognize the need for further improvement and are working hard toward that goal,” Hinkle concluded.

The report also found administrative judges used “cut and paste” images of medical records in favorable award decisions instead of including written analysis and failed to hold proper hearings -- "preventing them from collecting objective and useful information.”