An independent group recently determined that foreign trips taken by House Members and their staff over the past 11 years cost taxpayers $24 million, but the actual tab would likely be many times higher if it included the largest expense of Congressional delegations traveling abroad: getting there and back.

In the vast majority of instances, the cost of airfare is not included in the dollar tally of Members’ and staffers’ trips because the Air Force provides the transportation. The Defense Department, not Congress, picks up the tab and the costs are not publicly disclosed.

The data compiled by PoliticalMoneyLine, a nonpartisan for-profit Web site that tracks money in politics, comprises more than a decade’s worth of travel disclosure reports, which committee chairmen file quarterly with the Clerk of the House. Those reports cover lodging, food and sundries such as ground transportation. If a lawmaker or staff member uses a commercial airline as part of the trip, that cost is also included.

But such accounting distorts any analysis of who spent what and prevents a real accounting of the total cost of Congressional delegations, according to Rep. Christopher Shays (R-Conn.).

In its study, PoliticalMoneyLine ranked lawmakers according to how many trips they took and how much they spent between 1994 and 2004. Shays, who sits on the Government Reform and Homeland Security panels, took a total of 21 trips in the past decade, putting him 45th on the list of all current and former lawmakers during that period. But he ranked ninth on the list of lawmakers’ spending, joining only seven other Members who spent more than $100,000 on foreign travel.

Relative disparities between the number of trips and total cost can be due to a variety of factors, including the remoteness of the location or a weak exchange rate. But Shays maintains that being listed among the top 10 lawmakers for spending on foreign trips is the result of a simple accounting problem — his travel on commercial airlines, often to expensive and difficult-to-reach locations, is reported, while the travel on military aircraft is not.

“I prefer to travel commercially because it provides more flexibility and often it is less expensive,” Shays said in a statement. “Just as the public has the right to know about commercial travel by Members of Congress, travel with the Department of Defense should be disclosed and I would support efforts to do so.”

Judiciary Chairman Jim Sensenbrenner (R-Wis.) is listed as the lawmaker spending the fourth-highest amount on CODELs for the same reason. Sensenbrenner almost always takes commercial flights to his destinations, according to spokesman Jeff Lungren, which saves taxpayers quite a bit of money, but the savings are not reflected in the disclosure reports.

Many others at the top of the list of lawmakers spending the most also took commercial flights for a significant portion of their trips.

Rep. Mark Kirk (R-Ill.) said he believes military planes are used in large part because Members can take their spouses if there are empty seats. (Spouses are responsible for their own per diem expenses.)

But flying commercial is “generally one-tenth of the cost of traveling on a military plane,” Kirk added. “It’s far less expensive for the taxpayer.”

Data obtained by Roll Call in 1996 under the Freedom of Information Act indicates that the cost of the Air Force transports could be in the tens of millions of dollars, if not more, likely dwarfing the $24 million figure reported by PoliticalMoneyLine. The cost of military transports for just nine CODELs in 1995 amounted to nearly $1 million, according to Air Force records.

A spokeswoman for the Defense Department said that updated “information is not readily available.” Requests for such data would have to be submitted under FOIA, she said, adding, “it will not be a quick process.”

Shays isn’t the only one concerned about the diverted accounting.

“What Congress is generally doing is shifting the expenses to another branch,” said Pete Sepp, spokesman for the National Taxpayers Union. “It’s almost a classic exercise in the various branches of government deferring to each other so much that no one is accountable. The State Department says, ‘We just do the setup.’ The Air Force will say, ‘We just fly them there.’ And Congress will say, ‘You’ll have to talk to the State Department and the Air Force.’”

The State Department’s Congressional Travel Office coordinates CODELs and provides logistical and diplomatic support once Members and staff have arrived at their destinations. The acting director of the Bureau of Legislative Affairs, Will Steuer, said State “facilitates” the trips, but the department has “an internal policy not to discuss anything to deal with CODELs. We protect the privacy of Congress.”

Amy Keller contributed to this report.