Settlers of Catan has plenty of expansions that change the dynamics of the game, forcing the players to work together, putting a focus on exploration, or drawing emphasis to a certain section of the map. A new variation from publisher Mayfair Games will add a new wrinkle to the basic game, allowing some players to get a boost from their oil fields at the possible cost of ruining the entire island of Catan.
The Oil Springs variant essentially moves the game into a modern era. No more knights and barbarians. The key differences are that three hexes will have oil fields on them (including the desert), and there's a third level of settlement advancement, the metropolis. If a hex with an oil field on it is rolled, it will produce its normal production and also an oil token. Oil tokens can be traded in for two of any other resource, or you can combine them with other resources to upgrade a city into a metropolis. A metropolis is worth three victory points, produces three resources, and is immune to coastal flooding, which I'll explain in a second.
This boils down to a new, powerful resource than can greatly accelerate advancement in the game, or allow a faltering player to come from behind. What's the catch? Every five times someone uses an oil token, an environmental disaster occurs. Two things might happen: coastal flooding, in which settlements built on the coast are wiped out and cities are downgraded to settlements; or one hex on the board will incur industrial pollution and will no longer produce any resources for the rest of the game. If five hexes are wiped out, the island becomes uninhabitable due to pollution and everyone loses.
There are a few other rules that make this interesting. For one thing, there's a finite amount of oil, so the oil springs will not necessarily produce all you need. However, oil counts as a resource when the Robber strikes, and there's a limit to how much you can hold. That means no one can just horde all the oil. Finally, players can flip over one of their oil tokens each turn, sequestering it instead of using it. If you flip over three, you get the Champion of the Environment token, worth a victory point (you also get a VP per three sequestered oil tokens). Other players can steal the Champion token by being even more environmentally awesome than you are, just like with Longest Road.
I know some players are going to balk at what they see as some kind of liberal, environmentalist agenda here, but these new mechanics actually address a real problem that we encounter very often in the real world. It's called the Tragedy of the Commons, and it definitely plays a big part in environmental and economic problems. The problem is that multiple individuals (or groups) sharing a finite set of resources will tend to use as much of that resource as possible for their own benefit, even though it may destroy the overall resource supply, which ultimately harms everyone.
The best example of this is fishing. If there are no legal limits set on fishing, each individual fishing boat will catch as much fish as possible every year. They know that this will ultimately harm the fishery, prevent the fish population from recovering, and destroy their livelihood in a few years when all the fish are gone. However, they know that if they don't overfish, other fisherman will, so the fishery will be destroyed anyway. Therefore, they might as well overfish now and enjoy the abundance while it lasts. It's why government regulations are necessary (and the biggest flaw with strict libertarianism, frankly). The Champion of the Environment token, in this case, acts as a brake on overuse of oil. Also, your friends hating you because you keep destroying Catan acts as a brake as well.
The really cool thing about this expansion is that you can download the rules and the printable tokens for free at the Mayfair website. They'll be releasing a printed version for sale at some point.