Canadian members of Parliament are spending less on travel but office budgets nonetheless continue to increase – due largely to the ballooning costs of staff salaries, taxpayer-funded advertising and constituency mail campaigns.

Financial documents released Monday reveal MPs' yearly spending in further detail than ever before. It comes at a time when the spending of MPs and senators is under mounting scrutiny, with RCMP investigating the claims of some senators.

All the MPs' spending was approved by the House of Commons, which sets limits on how many flights they can take and what their offices can spend, depending on the size of their riding. The spending of each MP varies substantially.

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Total spending for all MP offices between April 1, 2012, and March 31, 2013, was $123-million, up from $121-million the year before. Roughly half of the spending was on staff salaries, with the rest spent on travel, office supplies, advertising and a residence in Ottawa.

Of the three biggest party caucuses, the Liberals averaged the highest spending at $404,365, followed by the Conservatives at $398,235 and the NDP at $394,477, a Globe and Mail analysis shows.

Spending on advertising, household mail-outs and so-called "10-per-centers" – direct-mail campaigns that typically target a specific issue for only certain constituents – were all up from the year before, while spending on constituency offices, furniture, telecommunications and office materials all decreased.

The disclosure standards are part of "a move for ongoing improvement of transparency," said Laura Smith, a spokesperson for Conservative Whip John Duncan, who sits on the board of internal economy that oversees MP spending. "Work is ongoing. This is a continuous process," she said.

MPs from the Prairies were the five biggest travel spenders, led by Alberta Conservative Blake Richards at $132,227. Saskatchewan Conservative Garry Breitkreuz, Alberta Conservative Brian Storseth, retired Manitoba Conservative Merv Tweed and Saskatchewan Liberal Ralph Goodale rounded out the top five travel spenders, each of them claiming at least $125,000 on their own travel, excluding that of staff and family.

NDP MPs spent, on average, the most on ads compared with the two other biggest parties – $20,114 per MP, ahead of the Conservatives' $14,224 average and the Liberals' $12,598 average.

A total of 86 MPs spent at least $25,000 per year on conventional advertising – 44 New Democrats, 31 Conservatives, six Liberals, three Bloc Québécois members and two Independents. The biggest spenders were two Northern MPs: Conservative Environment Minister Leona Aglukkaq and NDP MP Romeo Saganash each spent more than $35,000.

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While NDP MPs dominated conventional ad spending, Conservatives dominated the list of major users of 10-per-centers. Conservative MPs spent an average of $6,601 on the mail-outs, while the NDP averaged $5,272 and the Liberals averaged $1,064.

A total of 21 MPs spent more than $15,000 on the 10-per-centers – 16 Conservatives and five New Democrats. Ontario Tory MP Kyle Seeback led the way, with $32,115 in 10-per-center spending. Transport Minister Lisa Raitt spent $20,480 on the mail-outs, the fourth-highest total, while NDP MP Olivia Chow spent $19,898, the most of any non-Conservative.

On household mailouts – which are sent to every home in a riding no more than four times a year – the NDP averaged $13,861 per MP in spending, ahead of the Conservatives at $12,779 and the Liberals at $12,210.

The spending disclosure rules date back to 2000, but have been occasionally expanded. This year's disclosure separated out travel claims of MPs, dependents and other designated travellers, and also specified each MP's claims for "secondary housing" – or lodging in Ottawa. Of the three biggest parties, the Conservatives spent the most, on average, on a secondary residence, at $15,253. The Liberals averaged $14,729 in secondary residence spending, while NDP MPs averaged $12,760.