[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2008/images/09/12/art.bidenstlouis0912.ap.jpg caption="Sen. Biden campaigned in St. Louis earlier this week."]
(CNN) - Joe Biden's newly released tax returns appear to confirm what the Democratic VP candidate has long contended - he is among the poorest U.S. senators currently serving.
At least half the nation’s senators are millionaires. But Biden and his wife Jill earned a relatively small $320,000 in 2006, paying about $66,000 in taxes. Over the last 10 years Biden and his wife earned just shy of $2.5 million - an average income of roughly $245,000 per year.
The Obama campaign released the 10 years worth of documents earlier Friday, in part to pressure the McCain campaign to do the same with Sarah Palin and her husband Todd's returns.
“The last eight years have brought Americans' faith in their government to its lowest point in over thirty years," Obama spokesman Josh Earnest said. "The only answer is to change the way we do business in Washington. That starts with something as simple as transparency. That's why Senator Biden is releasing his tax returns for the last 10 years."
A McCain aide told CNN Friday the campaign would release Palin's documents, but on their "own timeframe."
The Bidens' returns do not specify the various sources of the income, but the Delaware Democrat earns $165,000 per year as a senator and draws roughly $20,000 annually from his visiting law professorship at Widener University. Jill Biden is a teacher in Delaware and draws a salary of about $66,000. The 2007 tax returns also indicate Biden earned $71,000 in royalties for his book "Promises to Keep."
Biden, who does not hold a second residence in Washington and commutes back to Delaware daily via Amtrak train, often jokes about his relatively poor financial standing on the campaign trail. His modes net worth is also touted by the Obama campaign as a sign Biden has not become a creature of Washington or a fixture on its cocktail circuit.
"I make a good salary, although I am listed as the second-poorest man in this Congress," Biden said in Missouri last week. "I’m not proud of it. I’m not proud of it. But that’s what happens when you get elected when you’re 29 years old."
The newly released tax returns also show the Bidens have given substantially less to charity as a proportion of their income than both Barack Obama and John McCain. In 2007, Biden donated $995 to charitable organizations, or 0.3 percent of his pre-taxed income. That compares to the 5.7 percent of income the Obamas donated to charity last year and the 26 percent John McCain gave away.
As a U.S. senator, Biden released a financial disclosure form earlier this year in which he valued his assets at between $59,000 and $360,000. He also reported liabilities of between $140,000 and $365,000.
"When the last listing came out, they listed my net worth as between 70 and 150,000 dollars and Rush Limbaugh said ‘How can this guy manage our economy, he doesn’t have any money?’" Biden also said at that Missouri campaign stop. "Well, I thought the deal was, when you went to work for the government you weren’t supposed to make money!"