That is a good question, one that I have never bothered to find out. Seems to me that the little 533 1-brnr stove was one of the first true duel fuel stoves that Coleman started to market, around the late 80s perhaps starting in the 90s but I can't be sure, followed quickly with the suitcase models. The earliest that I have been able to find out is around 1993 but they may have come out sooner than that. I just don't know. Hopefully, someone can chime in with some more info. Perhaps one of us can write Coleman to see when they started marketing duel fuel stoves. Sorry I couldn't be of further help.