U.S. Sen. Mary Landrieu, D-La., raised $2.7 million for her re-election campaign from July through September, outpacing the fundraising of her best-financed Republican challenger, U.S. Rep. Bill Cassidy, of Baton Rouge, according to campaign finance reports and news releases.

But Cassidy reported $4.4 million in cash on hand for the balance of the election campaign — $900,000 more than Landrieu has on hand. The amount Cassidy and Landrieu each has available to spend before the Nov. 4 open primary may actually be somewhat closer to even, because of rules about when certain contributions can be spent.

The Cassidy campaign said it raised $2.5 million in the July-September reporting period.

Landrieu’s quarterly take brings the total amount she has assembled for her official campaign to $16.2 million since her last election, in 2008. The equivalent amount for Cassidy is $10.5 million since his last election, in 2012.

The third Senate candidate running a seven-figure campaign, tea-party Republican Rob Maness, reported raising $1 million in the three-month period, with $390,000 on hand. Maness is a retired Air Force colonel from Madisonville making his first run for elective office. His total for the campaign is just over $2.3 million.

If, as polling indicates, no candidate wins a majority of the Nov. 4 vote, the top two finishers will meet in a Dec. 6 runoff. That matchup likely will pair Landrieu and Cassidy, according to recent polls, which show Landrieu leading the open primary field but trailing Cassidy in a theoretical runoff.

The election is one of the highest-profile Senate races in the country, because Republicans have targeted Landrieu — the sole remaining Democrat elected statewide in Louisiana — in their effort to pick up the six seats they need to gain a Senate majority. Cassidy is the favored candidate of the Republican establishment.

Candidates for the U.S. Senate and House file fundraising reports with the Federal Election Commission every three months. The July-September reports are due Wednesday, but only House candidates are required to file electronically, and their full reports are immediately available online. Senate candidates may file by mail, and the reports may not be posted online for several days after the deadline. Cassidy and Maness provided copies of their FEC summaries, while the Landrieu campaign issued a news release Wednesday.

Because of the idiosyncrasies of the Louisiana election system, the candidates last filed reports for the period from July 1 to Aug. 2, but the fundraising totals above represent amounts for the full July 1-Sept. 30 quarter.

Exact comparisons of the cash on hand available for the Nov. 4 vote cannot be made from the summary reports, because some of the money collected by the candidates can be spent only on a runoff, if there is one. On Aug. 2, Cassidy reported $5.6 million in cash on hand compared to Landrieu’s $5.5 million, but hundreds of thousands of dollars of Cassidy’s total cannot be spent before a runoff, while a far smaller amount of Landrieu’s Aug. 2 total was in that restricted category.

The reports include only the activity of the official campaign committees. Those committees, controlled by the candidates, are required to itemize contributions and expenditures. Contributions may be accepted only from individuals and political action committees, and the FEC sets maximum allowable amounts for each contribution. Donors of more than $200 must be identified.

But that represents only a portion of the money flowing into the election. Millions of dollars more spent on political advertisements fall under the category of “outside expenditures,” which is spending by groups and organizations who by law may not coordinate their activities with the official campaigns, but who advocate for the election or defeat of a specific candidate.

Those groups fall into different categories, and are subject to different rules for disclosure and activity. Most can accept unlimited contributions from any source.

As of Wednesday, outside expenditures totaled $7.3 million either for Landrieu or against Cassidy, according to the website OpenSecrets.org, which bases its accounts on FEC information. Spending for Cassidy or against Landrieu totaled $4.3 million. In addition, outside spending specifically supporting Maness amounted to just under $400,000.

Beyond that, organizations have spent money in Louisiana on advertising that criticizes or praises a candidate or issue without explicitly urging a candidate’s victory or defeat. That spending is not reported to the FEC unless it occurs within 30 days before a primary or 60 days before a general election.