— Bernd Debusmann is a Reuters columnist. The opinions expressed are his own. —

The Pentagon has an evocative term for the level of spending on a war: burn rate. In Afghanistan, it has been running at around $5 million every hour for much of the year. The burn rate will begin going up next week when the first of an additional 30,000 U.S. troops arrive.

Once they are all in place, the burn rate is estimated to exceed $10 million an hour, or more than $8 billion a month. Much of that is literally burned — in the engines of American jeeps, trucks, tanks, aircraft and power generators. On average, each of the 183,000 soldiers currently deployed in Afghanistan and Iraq requires 22 gallons of fuel a day, according to a study by the international accounting firm Deloitte.

Because of a difficult and dangerous supply line that runs more than 1,200 miles through Pakistan, fuel for the troops in Afghanistan is considerably more expensive than for those in Iraq: an average of $48 per gallon counting the cost of transport and protection. Flown by helicopter to positions on remote Afghan front lines, the cost can reach $400 per gallon.

Which helps explain why Afghanistan “is one of the most expensive, perhaps the most expensive, war in U.S. history on a per troop basis,” says Todd Harrison of the Center for Strategic and Budgetary Assessments, a Washington think tank. His estimate of the cost per year of a soldier deployed in Afghanistan this year matches the number used by the White House – around $1 million. (The Pentagon says is it is less.)