| 1920 |
The 19th Amendment to the Constitution of the United States granting women the vote is ratified. |
| 1921 |
Insulin discovered by Frederick Banting at the University of Toronto, a discovery that has saved millions of lives. |
| 1922 |
Benito Mussolini comes to power in Italy. |
| 1923 |
Cecil B. DeMille, Hollywood director and producer, films the silent movie, The 10 Commandments. |
| 1924 |
Communist leader Vladimir Ilich Lenin dies; Josef Stalin comes to power. |
| 1925 |
Cities Service begins drilling in the rich Seminole Field in Oklahoma using new tools and oil recovery techniques. |
| 1925 |
The Scopes "Monkey Trial" draws national attention-high school science teacher John T. Scopes goes on trial for teaching Darwin's Theory of Evolution, thus violating Tennessee's Butler Act. |
| 1926 |
Gene Tunney defeats Jack Dempsey to win the world heavyweight boxing title. |
| 1927 |
American singer and actor Al Jolson stars in The Jazz Singer, the first feature-length film to successfully integrate sound. |
| 1927 |
All the Cities Service subsidiaries combined had, or were drilling, 176 wells and producing 160,000 barrels per day. |
| 1927 |
American aviator Charles Lindbergh makes the first nonstop, solo flight across the Atlantic Ocean. |
| 1927 |
Cities Service consolidates all the gas producing and transportation activities of the Empire Company into the Cities Service Gas Company. |
| 1927 |
Cities Services introduces the high octane "Koolmotor" gasoline along with its companion "Koolmore" motor oil. |
| 1928 |
Cities Service discovers the famous Oklahoma City Pool, one of the largest and most productive oil fields of the time. |
| 1928 |
Cities Service merges with Arkansas Natural Gas and its subsidiaries, Ark Fuel and Louisiana Oil Refining. |
| 1928 |
Walt Disney produces first sound cartoon. |
| 1929 |
Stock market crash leads to the Great Depression. |
| 1929 |
Future President of Cities Service W. Alton Jones buys $50 million worth of utilities. |
