Police said it is not clear where exactly the shooting took place, but HPD found the young man on the South Loop near Telephone Road around 11:40 p.m.
The 18-year-old was driving when a gunman in another vehicle fired shots into his orange Dodge Avenger, HPD said.
Video from the scene showed bullet holes in the Avenger.
The victim's mom reportedly witnessed the shooting.
Officers believe a passenger in the suspect vehicle fired the gun, but there are possibly multiple suspects involved.
The 18-year-old was shot in the back and taken to Memorial Hermann in stable condition. He is expected to survive.
Police did not have a description of the suspect vehicle or any of its occupants.