Some Salt Creek oil wells in the 1910s and 1920s were uncontrollable gushers, and before pipelines, storage tanks, and advanced equipment, much oil soaked into the ground, ran into streams, and was burned to reduce runoff. A few early wells produced more than 5,000 barrels per day, which the ill-equipped companies pioneering the field struggled to control. Salt Creek production grew rapidly from the 1890s until 1923, when it yielded 35,000,000 barrels and was known as the richest field in the U.S. Declining production in 19214 signaled decreasing gas pressure and oil supply, and once oil stopped naturally flowing to the surface, wells were pumped. Through the 1920s, flowing wells were pushed to the surface by natural gas, and in 1916 Midwest Refining Company began building gas plants, booster stations, and pipelines to collect and transport that escaping gas, producing natural gasoline as a byproduct. By the end of 1925, practically every well in Salt Creek was on the pump, powered by a central steam-turbine, gas-fired electric plant near Midwest, making the field one of the first and largest totally electrified fields in the U.S.; the plant also powered the company refinery, new drilling, the local community, and lighting for a 1925 night football game, and it closed in 1958 but still stands. Since then, technological strides have transformed oil and gas production there from chaotic wildcatter operations into sophisticated systems, with new techniques tested continuously to extract oil from sand and rock. In the mid-1920s, natural gas was injected back into the ground to repressurize wells in a technique called gas drive; water flooding was introduced in 1955; other 1950s methods included hydofrac and fire drive; and in 1965 steam drive forced hot steam into underground sands to warm and release captive oil. Today, CO2 flooding is used throughout Salt Creek: carbon dioxide compressed into a liquid is injected underground alternately with water, then expands into a gas that forces oil from tiny crevices and micro-pores and pushes it to the surface, repressurizing wells so they again flow naturally. The appearance of the field changed repeatedly, from a forest of tall wooden derricks to lighter metal derricks beginning in the mid-1930s, then to pumpjacks and dense networks of power poles and cables, many of which are now disappearing as wells are converted to CO2 flooding, which also reduces the visual impact of production by repressurizing wells and piping oil and other products underground. More than 100 years after early expectations that Salt Creek wells would last 20 years, they are still producing, and with Casper refineries closed, Salt Creek oil now moves through underground pipelines to refineries in multiple states, where it is made into gasoline, kerosene, lubricating oils, petroleum jelly, heavy greases, paraffin, and coal tar; although Salt Creek is known for light oil, some wells produce heavy asphaltines, and its numerous oil-bearing formations yield a variety of crude types.