They will allow utilities to buy and sell permits to emit specific amounts of sulfur dioxide.

Beyond this they must buy extra permits.

They can buy or sell permits if they emit more or less of the gas.

Firms that need to increase their volume of emissions must buy permits from those who require fewer permits.

What's more, it allows individual utilities to buy permits from other power producers, or to bank excess compliance for future use.

And no state has ruled that utilities with the foresight to buy marketable permits cheaply will be allowed to keep the benefits.

Under the measure, restaurants would be able to buy $4,000 annual permits to sell beer and wine.

He added, however, that for the last year it had been possible for drivers to buy permits to run overloaded trucks on many highways legally.

Divers must buy seasonal permits for $25 to use the sites.

From April 2011, firms will need to buy permits for each tonne of carbon dioxide emitted.