Green group ranks oil and gas companies in Wyo.

A Laramie-based environmental group rated oil and gas companies operating in Wyoming on their environmental performance, ranking BP America Inc. as "best" and Encana Corp. as "worst."

The ratings were released Thursday by Biodiversity Conservation Alliance, which said it consulted with other Wyoming conservation groups to come up with the rankings.

"We considered in detail dozens, scores of companies," said Erik Molvar, a wildlife biologist with the Biodiversity group.

He said this was the first time his group had issued such rankings, and he didn't how often it will release the rankings in future years.

Companies rated as "best" were judged to be doing the most to move the industry toward minimizing the impacts of drilling on Wyoming's landscape and wildlife.

Biodiversity said BP employs the best environmentally friendly practices by drilling multiple wells from a single drilling pad through directional drilling and limiting wasteful venting of greenhouse gases. Directional drilling involves drilling wells at angles instead of straight down.

"It's always nice to be recognized for our efforts because we work so hard to do a good job minimizing our footprint," BP spokeswoman Paula Barnett said.

Shell and Bill Barrett Corp. followed BP on the "best" list.

The "worst" list consisted of companies that Biodiversity said have the greatest potential for improvement "due to their abysmal track record in Wyoming."

Biodiversity rated Encana as having the worst environmental practices mainly because of its dense drilling in Jonah Field in southwest Wyoming.

Biodiversity noted that Encana also was seeking to drill in Adobe Town, an area in southwest Wyoming that some conservation groups want to be preserved as a wilderness area.

Encana spokesman Randy Teeuwen said his company has pioneered various environmentally friendly techniques in Jonah Field, including the use of wood mats that allow vegetation to recover more quickly and flareless completions that reduce venting of pollutants. In addition, all but one of Encana's 11 drilling rigs in Jonah are powered by clean-burning natural gas, Teeuwen said.

"We clearly can point to many environmental innovations that we have been using in Jonah Field for the past three to four years that we feel puts us in a leadership role along with a lot of other companies who are using and innovating techniques that they have as well," he said.

Encana was followed by Anadarko and Yates Petroleum Corp. on the "worst" list.

Windsor Energy received a "dishonorable mention" for a gas well blowout that contaminated some underground water wells in northern Wyoming.