My favorite 18xx game for six players is two games of 1846 with three players each.
Malcolm C wrote:
The only way to be even more fuel efficient is to fuel a formation (which is in reserve) during the reaction phase in your opponent's turn. That fuel lasts throughout your opponent's player turn, and throughout your next player turn (ie movement and exploit phases) until your clean up phase.
And it could happen that your opponent gets a double turn, in which case it could last through your opponent's player turn and their next player turn, and then through your own subsequent player turn (not that you could take full advantage of that, but you might have a unit in reserve that gets fueled in one opponent player turn, stays in reserve, and then moves in the reaction phase of the second opponent player turn, and is still fueled for your own player turn.)