According to legend, Montana's first oil refinery was built in the Cat Creek area when John R. Hill, a local rancher, built a small facility out of parts scavenged from large steam-powered tractors. The more formal Weowna Refinery was built at the Cat Creek strike and was almost immediately removed to Winnett in 1921, at a site very close to the Chicago, Milwaukee & St. Paul railroad spur. That refinery would operate intermittently into the early 1930s.
The Great Northern Refinery, also an independent, shipped its first refined fuels from Winnett in November 1921. Yale Oil Company, a national concern, constructed a third refinery near Winnett in 1936, but it was dismantled about a year later when a bid for government land was lost to Continental Oil.
An astounding number of oil refineries were constructed in Montana during the early decades of oil development and they largely followed development of the state’s oil fields, beginning with Cat Creek and the larger Mosby Dome in the 1920s. These “tea kettle” refineries were installed close in to the oil strikes. Even by the standards of the day they were considered inefficient, as they skimmed gasoline off the light oils that sometimes yielded 50 percent. Remaining kerosene-type fuel oil could be sold to the railroad with some residual tars marketed locally.
The Sunburst and Kevin areas were exploited next in north central Montana, and would lead statewide production from about 1925 through 1935. A bit further west, the Pondera Field near Conrad was producing heavily in 1929. The Bannatyne Field north of Great Falls was discovered in summer, 1927. The Dry Creek Field just south of the Canadian border was developed in 1930 by the Ohio Oil Company. That field's early production was reportedly almost pure gasoline. Dry Creek Wells averaged about 4,500 feet, which was considered very deep at the time. The Cut Bank oil fields were developed in the mid-1930s and were considered high quality during the Depression era of limited demand. Oil extracted from those fields would lead state production well into the 1950s when oil was discovered in the Williston Basin around 1955.
Two refineries were built in Lewistown in 1921 and 1922 to process the light crude from nearby fields of the Mosby Dome. Lewistown Oil and Refining Company would later be purchased by Continental (Conoco) and the refinery there would operate until 1943. Arro refinery in Lewistown processed gasoline as well as fuel oil for the railroads during the oil-fired steam era. It would close in 1942.
The Sunburst-Kevin area saw refineries constructed in the early 1920s. Kevtana, later to become Big West, would operate for about 50 years. International Refining there would become Grizzly and later Texaco, operating until 1960. This era also saw the construction of refineries outside the immediate fields, most notably the Sunburst Oil and Gas refinery built in Great Falls in 1923. Butte had two oil refineries during this time and the Hart Refinery in Missoula was put up in 1924. Kalispell also had a refinery (Unity) that operated off-and-on until about 1960.
By 1929, consolidation and scale came to refining with only 13 operational refineries in the state, mostly serving local and regional markets. In that year, 85 million gallons of gasoline was used in the state, up about 75 percent from 1926. Automobiles and tractors were becoming more obtainable to Montana residents and agricultural business. Gasoline produced by the tea kettle refineries of the 1920s offered octane levels probably in the 55 to 70 range, adequate for most machines of the era. Charles Lindberg reportedly flew the Spirit of St. Louis in 1928 on 73 octane fuel – the highest quality then available.