Just before 2 a.m., the victim began arguing with a man at Harry's Sportsman Lounge at 833 Texas St., Fairfield police said.
The two left the bar and continued their argument outside, where the suspect went to the cab of his truck and retrieved a handgun.
The suspect then shot the victim in the upper left leg and drove away before police arrived. The victim's injuries were not life threatening, police said.
Officers were not able to find the suspect, who is described as a white man in his 50s with a thin build and long, straight hair. He has a multi-colored, goatee-style beard, police said.
The suspect's vehicle is described as a late 90s model Ford F150 truck with an extended cab. It has a tan colored camper shell and possibly Nevada license plates.
Anyone with information about the incident is asked to call Fairfield police at (707) 428-7300 or Solano County Crime Stoppers at (707) 644-STOP.