Nearly 100 allegations of senatorial misconduct were made in 2009, and 13 preliminary investigations over potential breaches of Senate ethics rules were launched, according to a report issued Friday by the Senate Select Committee on Ethics.

The committee says after it launched the preliminary inquiries, it dismissed eight of the ethics complaints, and issued one letter of admonition, suggesting that the secretive panel is now investigating four separate incidents involving members of the Senate or their staff. The committee, which is evenly divided between three Republicans and three Democrats and chaired by Sen. Barbara Boxer (D-Calif.), released Friday's annual report to comply with a requirement under a 2007 transparency law.

While the report does not name individual senators, several sources say that there is an ongoing investigation into Sen. John Ensign's affair with an ex-staffer, and that the committee has issued several subpoenas to key figures in the scandal. The Nevada Republican has denied any wrongdoing in the matter, which involves payments made to the couple at the heart of the scandal as well as questions over whether the senator ran afoul of ethics laws in assisting with the lobbying career of the aggrieved husband of the senator's former mistress.

Sen. Tom Coburn (R-Okla.), who was Ensign's roommate and provided guidance to the senator during the affair, has not yet been contacted by either the ethics panel or the FBI, which is also investigating the matter, he told POLITICO this week.

In its report, the committee said it received 99 complaints last year, not including the 26 carried over from previous years. It said that it had dismissed 58 of those complaints because there would be no violations of Senate rules even if the allegations were true, and also rejected 45 others because they lacked sufficient facts to warrant an inquiry.

Last year, the Senate panel dismissed charges lingering for a year against Sens. Kent Conrad (D-N.D.) and Chris Dodd (D-Conn.) over whether they received special interest rates from Countrywide Financial, saying they should have “exercised more vigilanceâ€