OKLAHOMA CITY - The American Humane Association and PETA have strongly stood against the use of gas chambers.

In addition, a petition on change.org that calls for banning of gas chambers has received thousands of signatures. But some shelters in Oklahoma haven't stopped.

"The animal does not lose consciousness and brain function until after the vital organs shut down," said Cynthia Armstrong, Oklahoma Director of the Humane Society of the U.S.

Armstrong and the Humane Society of the U.S. recommend lethal injection to euthanize animals.

"Much quicker, less stress, pain free," said Armstrong.

But Oklahoma remains as one of eight confirmed states to still use gas chambers. Shawnee is just one of five confirmed cities that use a gas chamber.

Shawnee Administrator of Support Services Chris Thomas said in a statement:

"We wish we would not have to euthanize at all. Even though our adoption rate is around 44% throughout the year, due to economics we do use gas. When you don't have a big tax base, you have to do what you can within your means."

In a 2009 study from the Humane Association in North Carolina, the cost of injection compared to gas, is more than two dollars less per animal.

Thomas's response to that study:

"There's more to it than just the cost of the medicine for injections. Overall, we as humans cannot kill the problem away."

"We want that death to be as humane and painless as possible," said Armstrong.

Members of change.org agree with Armstrong. A petition was started to have Oklahoma pass legislation banning euthanasia by gas chambers. The petition already has more than 5,000 signatures.

"There's definitely support for this change and it would be a positive one for the animals and the shelters and their image as well," said Armstrong.

Other cities confirmed to us they still do euthanize by gas chamber: Cushing, Poteau, Broken Arrow for what it calls "extreme cases", Sayre and Clinton.

Sayre city officials say they only use their chamber to kill skunks. Clinton officials say they hope to change from gas chamber practices within the next few months.