Chris Miller nearly doubled his $3,500 stock investment in a renewable-energy firm in 2008. It was a perfectly legal bet, but he's no ordinary investor. Mr. Miller is the top energy-policy adviser to Nevada Democrat and Senate Majority Leader Harry Reid, who helped pass legislation that wound up benefiting the firm. Mr. Miller isn't the only Congressional staffer making such stock bets. At least 72 aides on both sides of the aisle traded shares of companies that their bosses help oversee, according to a Wall Street Journal analysis of more than 3,000 disclosure forms covering trading activity by Capitol Hill staffers for 2008 and 2009. The Journal analysis showed that an aide to a Republican member of the Senate Banking Committee bought Bank of America Corp. stock before results of last year's government stress tests eased investor concerns about the health of the banking industry. A top aide to the House Speaker profited by trading shares of Freddie Mac and Fannie Mae in a brokerage account with her husband two days before the government authorized emergency funding for the companies. The aides identified by the Journal say they didn't profit by making trades based on any information gathered in the halls of Congress. Even if they had done so, it would be legal, because insider-trading laws don't apply to Congress. Unlike many Executive Branch employees, lawmakers and aides don't have restrictions on their stock holdings and ownership interests in companies they oversee.