The debate over Pentagon spending is hardly new, but it has picked up again after President Trump requested an additional $52 billion in funding for the Pentagon. Fiscal hawks are skeptical about large budget increases after reports this January that leaders had buried an internal study exposing waste throughout the department, not to mention the longtime failure to pass an audit.

Now, evidence has surfaced that the department has raised $6 billion over 7 years by charging excessive fuel prices to its armed forces. The Washington Post reports:

Since 2015, the Defense Department has tapped surpluses from its fuel accounts for $80 million to train Syrian rebels, $450 million to shore up a prescription-drug program riddled with fraud and $1.4 billion to cover unanticipated expenses from the war in Afghanistan, according to military accounting records.

These prices rise because the Pentagon uses a system dating back to WWII, originally intended to improve efficiency and stop duplication: It buys fuel centrally and sells it back to the armed services and other customers at a fixed price. The problem? This price is often high above market rate, sometimes as much as a dollar per gallon.

Deputy Defense Secretary Robert O. Work and other Pentagon leaders object to any suggestions that this overcharging is done on purpose. They say it’s the natural result of fluctuating fuel prices. Other military leaders, though – especially in the Navy – have been criticizing this setup, with former Navy Secretary Ray Mabus calling it a “slush fund.” These allegations call to mind the other notorious slush fund in the Pentagon, the overseas contingency operations budget.

What’s not up for debate is just how much inefficiency and waste is in this department just like any other part of government. Without passing an audit and pushing for real reforms, adding dramatically more money to the budget should make every fiscal conservative and every defense hawk pause, because there is no guarantee the new funds will be used properly or really provide for the common defense.

This post originally appeared at the Institute to Reduce Spending.