How do I know what kind of gas my airsoft gun uses?

I recently bought a KJ Works Match 15 Metal Slide & Barrel Gas Blowback Airsoft Pistol. Neither the manual nor the site I bought it from tells me what kind of gas to use. I'm afraid to use propane if it uses something like CO2 or green gas. This is my first gas powered airsoft, I've got mostly electric. I'm reaching out to my fellow airsoft enthusiasts. Please help me out here, I'm itching to use this baby.