Yellowstone National Park has released its latest range of possibilities for future snowmobile use in the park, ranging from allowing 720 machines a day to an outright ban.

The dispute over snowmobiles in the nation's first national park stretches back a decade, pitting snowmobile manufacturers and users against environmentalists who want them gone from the park.

The six alternatives released Thursday, none of them new, will set the parameters for a new Yellowstone snowmobile study slated for release in early 2011.

If a new rule for snowmobiles is not adopted by winter 2011 and a temporary rule allowing 318 snowmobiles a day is not extended, the machines will be barred from the park until a rule is adopted.