by Barbara Pepper Rotness, MHS Reference Assistant
It is generally accepted that the first discovery of oil in Montana was made on August 10, 1864, twelve and a half miles from where the Bozeman Trail crosses the Big Horn River. Although not sufficiently documented to earn its place as the first, an earlier sighting was mentioned by William Aldridge. In 1855, he and his party of emigrants, heading northward, spotted oil seepages - one at Soap Creek and one at the Musselshell crossing. And in May 1880, Granville Stuart was scouting out a new cattle range in the Musselshell River area and proclaimed "there are petroleum indications all through here and someday Montana will produce oil but it is worthless now." There had been various areas throughout Montana considered to have oil producing potential and when drilling first began in 1901, many of those areas were tapped. None of these sites proved lucrative, and it took two more decades before that potential was realized.
Photo of oil pond at Cat Creek Field 
In late 1919, near Winnett, Montana, the Frantz Corporation began oil exploration on a creek flowing into the Musselshell River, and on February 19, 1920, the company drilled the well that established Cat Creek as Montana's first commercially productive oil field. Curley Meek, one of the first drillers in the Cat Creek area, was later quoted in a February 24, 1964, Great Falls Tribune article, "there was no place to store the oil, so it was dammed up in a coulee and given away to ranchers and farmers as sheep and cow dip until they began using it in their cars."
The situation of the initial drilling at Cat Creek was further described in Pages of Time: A History of Petroleum County, Montana. "With no storage facilities available, oil flowed into a coulee where people from all over the countryside came to look at it...The oil was of such high gravity it could be used directly in tractors and even Model T's, and it was free to all comers. Tanks were immediately constructed, and during the summer Frantz Corporation laid a two-inch pipeline to Winnett."
Over the next few years, continued development of the Cat Creek oil fields resulted in an increase in the area's population and the legislature voted to form a new county. Sectioned off from eastern Fergus County and named for its successful oil production, Petroleum County officially became Montana's 56th and final county in February 1925.
 The Butte (Mont.)
Miner, April 22, 1923.
 Granville Stuart,
Forty Years on the Frontier (Cleveland, 1925), Vol. II, p. 124
 Petroleum County
Public Library, Pages of Time: A History of Petroleum County, Montana
(Lewistown, Mont., 1990), 140.