In each case, the suspect approached women as they were sitting in or walking to their vehicles, displayed a gun and took their car keys, Chicago police said.
A carjacking took place at 5:30 p.m. Tuesday in the 5200 block of South Drexel Avenue, police said. Another happened 15 minutes later in the 800 block of East 53rd Street.
The third occurred about 8:30 p.m. Sept. 30 in the 5000 block of South Blackstone Avenue, police said.
The suspect was described as 20 to 25 years old, 6-feet and 185-200 pounds with black hair. He was wearing a black or gray hooded sweatshirt and black sweatpants.
Anyone with information is asked to call Area One detectives at 312-747-8380.