Republicans' official effort to retake a majority in the Senate raised a record $15.5 million in September -- roughly four times its average monthly haul this cycle -- but officials Tuesday did not disclose how much money the committee spent last month or how much money it had saved for the final month of an already bruising campaign.

The National Republican Senatorial Committee's summary of September finances included only how much it had raised and suggestions that much of it came from online donors. The full report is not due until Oct. 20 and officials declined to release detailed figures.

"Over the last 20 months, we've revamped NRSC's direct mail technologies and invested heavily in building a more robust digital operation that has successfully tapped in to the grassroots energy and enthusiasm that's out there to shake up the Senate," said Sen. Jerry Moran, the Kansas Republican who leads the campaign committee.

The Democratic Senatorial Campaign Committee said its figures were not yet ready for release.

Senate Republicans have consistently been outraised by the Democrats. Heading into September, the NRSC raised an average of $4.1 million each month, which the DSCC raised about $6.6 million.

Senate Republicans said the sudden spike in fundraising suggests optimism among rank-and-file party members that the odds are improving that they might pick up the net six seats needed to tip the balance of power in to the GOP.

Without September's figures, the NRSC raised about $82 million to the DSCC's almost $112 million.