National Observer has learned that Conservative finance minister Joe Oliver has the most expensive costs in flights among all the members of Stephen Harper's cabinet, sometimes spending over $6,000 on a domestic plane trip between major Canadian cities. National Observer reviewed public records published on federal government websites to review Conservative spending on travel as Conservative leader Stephen Harper prepares to face his rivals on the economy at the Globe and Mail debate this evening. Here's what those records show...

Expensive flights to Calgary Records show that Oliver had the most flights costing over $4,000 between 2012 and 2013 for domestic flights from Ottawa to both Alberta and British Columbia. While he was natural resources minister in 2012, Oliver once billed $6,701 for a Calgary-bound flight to speak at an annual oil conference to the Canadian Energy Research Institute (CERI). While a search on Air Canada reveals that flights can cost up to $7,000 if booked a few hours before departure and in business class, the cost was significantly more than other ministers billed for similar trips. Other ministers including health minister Rona Ambrose and agriculture minister Gerry Ritz flew to Calgary for under $1,300 in 2015. On a number of occasions, Oliver's domestic flight cost more than a normal economy class round trip between Ottawa and Melbourne, Australia, (around $4,600) or a business class flight from Ottawa to Paris, France.

Search results on WestJet show only a few results of round trips from Ottawa to Calgary would cost in the $6,000 range, even if the flight was booked just a day in advance. A standard economy class ticket was under $1,300. Screenshot from Natural Resources website. Screencap of return flight from Ottawa to Calgary on WestJet. However Oliver is hardly alone in billing for costly flying expenditures. Public works minister Diane Finley booked a round trip to Vancouver for $7,221 in October 2014, and former minister of state for finance Ted Menzies — who is no longer an MP since accepting a lobbying position — flew to Victoria for nearly $7,200. During his one-day trip, he also billed $223 for meal costs. Ted Menzies' expenditure record. Spending taxpayer dollars within means? In 2006, Conservative leader Stephen Harper was elected on the promise to "end the culture of entitlement" in Ottawa, but the records of travel expenses by his hand-picked cabinet show that ministers frequently chose more expensive options when traveling domestically. Shortly after taking over the job as finance minister in March, Joe Oliver wrote an impassioned op-ed about fiscal responsibility and balancing budget.

"Canadians expect their government to spend within its means," he said. "After all, government cannot indefinitely spend more than it earns." In an impassioned speech before the Empire Club of Canada in Toronto in 2005, Harper pledged that he would enforce discipline and fiscal responsibility in federal government. "I have told my own MPs and parliamentary staffers that if they have ambitions to use public office to advance their own interests, or get rich lobbying a future Conservative government, they had better make different plans, or leave," he said.

Joe Oliver's office was contacted early this morning for comment on this article, but has not yet answered.