Cat Creek #1 well. Oil was discovered numerous times in Montana prior to 1919, but it wasn't until Frantz Oil Corp. struck "black gold" in December 1919 that the industry began to boom.The Denver-based company found the high-quality crude at ex¬tremely shallow depths in the Cat Creek field in Petroleum County east of Winnett. The easy access combined with the fact that the oil yielded about 50 percent gasoline made the venture remarkably prof¬itable for Frantz Oil. Well production began in Febru¬ary of 1920, and its success drew oil companies from around the region to the Cat Creek field. Throughout the year, nearly 60 rigs went into operation in the field and produced $734,181 worth of oil by the end of the year, according to a report by the Montana Oil Conservation Board.