From GEWar Manual
Armies need oil to move. The bigger the army, the more oil. Figures quoted here are for army sizes of 100t.
Any movement will instantly deduct 2 barrels of oil from your inventory. If you don't have that amount: no movement is possible.
The Oil consumption of moving armies is 2 barrels per 5 minutes.
Change of destination
An army can be diverted elsewhere while travelling from one city to another. 2 barrels of oil will be deducted at the time of diversion. Again, insufficient oil stocks = no movement.
No further oil is deducted for the original waypoint.
When your oil reserves run out (less than 2 barrels), the game buys oil from your cash reserves. Oil is purchased for you at a fixed rate of one geo per barrel. If you have 5 armies on the move, 10 barrels are purchased.
You are best off looking at the oil (black) market to find a better rate that 1 geo/barrel.
When your cash reserves run out, your army sizes begin to reduce. The army with the highest number of troops is hit first. 10 troops leave per barrel of oil required.
No Cash No oil
the army remains stationary until oil and / or cash become available.
Because the displayed game works in 6 minute time slots, you may arrive at your destination in 22 mins (eg) or 28 mins (eg), depending on the point in the cycle when you first started the move.