Shell Development Company was formed in 1928 to conduct petrochemical research. The following year, after the discovery of chemicals that could be made from refinery byproducts, the Shell Chemical Company began its manufacturing operation. By 1929, Shell gasoline was being sold throughout the United States. Although the economic problems of the early 1930s forced the company, along with the entire oil industry, to reassess and curtail its operations to some degree, Shell continued its chemical research. This resulted in the opening of two plants for manufacturing synthetic ammonia in 1931 and for making synthetic glycerin in 1937.