What do veterinarians use to put dogs to sleep?

My family dog of twelve years had to be put to sleep yesterday (yellow lab, he stopped eating and was having trouble getting around, hip problems etc). My parents asked me if I wanted to go with but I respectfully said no as I no longer live with them (on my own now) and he really is more of my mother's dog. Is the chemical concoction similar to the three drug course given for lethal injections? Is there anesthesia? Did my dog feel pain or go peacefully? Thank you for your time in advance.