World War II greatly stimulated the demand for petroleum products, especially high-octane aviation fuel and jet fuel. Phillips turned to technology to increase the octane rating of fuels for use in advanced engines. The company invented an HF alkylation process in 1940. The American petrochemical industry took off, first making such as styrene, ethylene, propylene and butadiene. After the war, it formed a subsidiary, Phillips Chemical Co., which entered the fertilizer business by producing anhydrous ammonia from natural gas. The company then built a complex on the Houston Ship Channel devoted to making petrochemicals and polymers.