Sen. Barack Obama saw a surge of interest in his writings as he drew closer to a presidential bid, earning more than half a million dollars in 2006 in royalties for one book and an advance for another, according to his financial disclosure report.

Obama received $572,490 for the books — one a best-selling memoir, "Dreams of My Father," and the other an account of his political journey, "The Audacity of Hope."

The memoir, published in 1995 in relative anonymity, enjoyed a resurgence in 2004 after Obama's speech to the National Democratic Convention in Boston. "The Audacity of Hope," published in October 2006, rapidly rose to the top of the New York Times best-seller list for nonfiction.

Obama reported receiving $147,490 in royalties for the memoir and a $425,000 advance for last year's book.

The report shows that he and his wife have assets of at least $455,000 in mutual funds, bank accounts and a pension from the Illinois Senate where Obama served from 1997 to 2004. The total amount is imprecise, however, because assets in the disclosure reports are catalogued in broad ranges.

But Obama's assets are far more modest than most of the other leading presidential candidates.

His report also includes notification of an agreement between Obama and Random House, the publishing house, of a $1.9 million advance for two nonfiction books, including "The Audacity of Hope," and a one children's book. The agreement was reached sometime before he took office in January 2005.

Obama had already made aspects of his finances public by releasing his 2006 income tax returns. He and his wife Michelle reported total income of $991,000 in 2006, including the royalties and book advance. In his disclosure, Obama reported that nearly $69,000 of the book money was used to pay related commissions and legal fees.

So far Obama is the only candidate to release his tax documents. Sen. Christopher Dodd, D-Conn., said Tuesday he, too, would make his tax returns public.

In other filings, New Mexico Gov. Bill Richardson, a presidential candidate who has called for a dramatic reduction in the use of fossil fuels, reported holding between $250,000 and $500,000 in stock options from North America's largest independent oil refiner.

Richardson, a Democrat, received the stock options from Valero Energy Corp. for serving on the company's board of directors from March 2001 to June 2002, according to a financial disclosure report he filed Tuesday.

Richardson also reported holding between $100,000 and $250,000 in Valero common stock and capital gains of between $50,000 and $100,000 from the sale of stock in Diamond Offshore Drilling Inc., a leading deep water oil exploration company.

In his report, Richardson, who was secretary of energy in the Clinton administration, said he intends to divest himself of the Valero stock if he's elected president. Valero is headquartered in San Antonio and Diamond Drilling is in Houston.

Republican presidential candidate Sam Brownback, an outspoken critic of the violence in Sudan, divested his stock portfolio of companies that do business with the African nation.

Brownback listed sales of nearly two dozen investments, several of which were mutual funds whose holdings include companies active in Sudan, according to a financial disclosure report he filed Tuesday. Among them was a mutual fund in the name of Brownback's wife valued at between $50,000 and $100,000. Other Sudan-related investments were in the names of the couples' children.

"Most of the movement of mutual funds in the portfolio was at the direction of the family to divest of Sudan-related investments," Brownback spokesman Brian Hart said.

Brownback also listed a blind trust held jointly with his wife that is valued between $1 million and $5 million. Last year, Brownback aides said he would seek legal advice on whether he could request that any Sudan-related investments be sold, but under the rules of the trust Brownback cannot be made aware of any transactions.

Democrat Hillary Rodham Clinton and Republicans Mitt Romney, John McCain, Tommy Thompson and James Gilmore all received 45 day extensions to file their reports. Other candidates filed their reports Tuesday and the Federal Election Commission's legal staff was reviewing them before making them public.