The US Department of Defense (DoD) is the largest oil consuming government body in the US and in the world
“Military fuel consumption makes the Department of Defense the single largest consumer of petroleum in the U.S” 
“Military fuel consumption for aircraft, ships, ground vehicles and facilities makes the DoD the single largest consumer of petroleum in the U.S” 
According to the US Defense Energy Support Center Fact Book 2004, in Fiscal Year 2004, the US military fuel consumption increased to 144 million barrels. This is about 40 million barrels more than the average peacetime military usage.
By the way, 144 million barrels makes 395 000 barrels per day, almost as much as daily energy consumption of Greece.
The US military is the biggest purchaser of oil in the world.
In 1999 Almanac edition of the Defense Logistic Agency’s news magazine Dimensions it was stated that the DESC “purchases more light refined petroleum product than any other single organization or country in the world. With a $3.5 billion annual budget, DESC procures nearly 100 million barrels of petroleum products each year. That's enough fuel for 1,000 cars to drive around the world 4,620 times.”
That budget increased a lot over the years. The US DoD spent $8.2 billion on energy in fiscal year 2004.
“In fiscal 2005, DESC will buy about 128 million barrels of fuel at a cost of $8.5 billion, and Jet fuel constitutes nearly 70 percent of DoD's petroleum product purchases.” says American Forces Information Service News Article by G. J. Gilmore. 
For some, this is not enough though. Here is what a report from Office of Under Secretary of Defense says “Because DOD’s consumption of oil represents the highest priority of all uses, there will be no fundamental limits to DOD’s fuel supply for many, many decades.” 
American GI is the most energy-consuming soldier ever seen on the field of war
“The Army calculated that it would burn 40 million gallons of fuel in three weeks of combat in Iraq, an amount equivalent to the gasoline consumed by all Allied armies combined during the four years of World War I.” 
In May 2005 issue of The Atlantic Monthly, Robert Bryce gives another example; “The Third Army (of General Patton) had about 400,000 men and used about 400,000 gallons of gasoline a day. Today the Pentagon has about a third that number of troops in Iraq yet they use more than four times as much fuel.”
The US military oil consumption overseas and the world oil demand
According to the Defence Logistic Agency’s Web Site, as of November 2005 more than 2.1 billion gallons of fuel have been used in support of Operation Enduring Freedom (since October 2001; war on terrorism in Afghanistan).
In the May 2005 issue of the Atlantic Monthly article Robert Bryce says that “The U.S. military now uses about 1.7 million gallons of fuel a day in Iraq. … each of the 150,000 soldiers on the ground consumes roughly nine gallons of fuel a day. And that figure has been rising.” This mean in Iraq each day 40 000 b/d of oil is consumed by the US military.
Yes, something is wrong with that figure. Compare it with the one given by the Defense Logistics Agency spokeswoman Lana Hampton. Accroding to an American Forces Information Service News Article she said the U.S. military is using between 10 million and 11 million barrels of fuel each month to sustain operations in Afghanistan, Iraq and elsewhere. This makes 330 000 - 360 000 barrel per day.
This is more than double the amount of oil used in the Gulf war!
According to a Rand Corporation report “1.88 billion gallons of fuel were consumed within the U.S. Central Command’s area of responsibility during Operations Desert Shild and Desert Storm (ODS/S), between August 10, 1990 and May 31, 1991.” . This makes 44.8 million barrels, or 150 000 barrels a day. Note that ODS/S lasted 295 days.
Moreover, “during ODS/S Saudi Arabia and the UAE supplied fuels without charge (1.5 billion gallons), whereas Bahrain, Egypt, Oman and Qatar charged for the fuels,” adds the Rand report.
Did Saudi Arabia and the UAE report that fuel as export? Did the US report it as import? Was it counted as Saudi or UAE domestic consumption? Or Was it counted as the US consumption?
I am afraid the answers to those three questions are No, No, No and No!
But that amount was surely counted in production.
My experience with international oil statistics tell me that the US military oil consumption overseas disappears in world oil demand. Hence, demand is understated at least that much.
Is about 350 000 barrel per day missing oil demand important?
 Presentation by American Petroleum Institute President and CEO Red Cavaney held at the USAF/API Awards Banquet – Arlington, Virginia, July 15, 2004. See also National Defense Magazine article in 2002.
 E. C. Aldbridge and D. M. Etter testimony before the U.S. Senate Armed Services Committee on June 5, 2001.
 American Forces Information Service News Article by G. J. Gilmore, DoD Has Enough Petroleum Products for Anti-Terror War, August 11, 2005. The article is posted also on DCmilitary
 More Capable Warfighting Through Reduced Fuel Burden, Office of the Under Secretary of Defense for Acquisition, Technology and Logistics, The Defense Science Board Task Force on Improving Fuel Efficiency of Weapons Platforms, January 2001,
 J.P. Stucker, J.F. Schank and B. Dombey-Moore, Assessment of DoD Fuel Standardisation Policies, Rand Corporation, 1994.