As other car companies moved from steam to gasoline power, the Stanley Steamer became the most popular steam powered car. As the internal combustion engine designs improved, however, steam and electric cars lost much of their popularity. Finally, the numbers of cars sold went down to less than 600 a year in 1918. That year the Stanley brothers sold the company to Prescott Warren, a Chicago businessman. both brothers retired. A few months later, while he was driving home from a trip to Maine, his car ran off the road. He was driving a new 1918 Model 735 Stanley Steamer. He died in the accident, July 21, 1918. He was 69 years old. His brother Freelan lived to be 91 years old.