Answer: Fuel, Fuel, Fuel
At takeoff the GlobalFlyer had 18,300 lbs of fuel on board.
The Williams International F.J.44-3ATW burns 295 lbs/hr. and will eventually slow fuel consumption to about 100 lbs/hr. as the flight progresses.
GlobalFlyer utilizes JP4 in the wing tanks and JP8 in the boom tanks. JP4 has better cold operation characteristics and it will take longer to gel. This is optimal for use in the wing tanks, as the fuel will be exposed to extremely cold temperatures at high altitude. The JP8 is used in the boom tanks and it is a highly refined fuel. JP8 was used instead of JET A because of the increased fuel density. This allowed more fuel to be placed in the boom tanks, increasing the distance the aircraft can fly.