Players are responsible for fulfilling the energy requirements for their countries throughout the years. Each year there are exactly enough resources to fulfill and the players have to decide which resources to claim for themselves. It's a simultaneous selection of the resources, so you don't know what the others are choosing. Sometimes you don't quite fill all your energy needs, so you have to buy resources from other players or the bank to cover. Action and event cards modify the energy market from year to year, and clever play of these cards can turn the tide of the game. The player with the most cash at the end of the game wins.
Even though the game says it supports up to 5 players, the fifth player's responsibility is to be the banker.