Spokesman Mark Plowden said Wednesday that Attorney General Henry McMaster has sent agents to stations and suppliers to determine when decisions were made to change prices, and by how much.
Gas prices shot up shortly before Hurricane Ike struck the Texas coastline and its oil refineries. State law allowed McMaster to criminally investigate the claims after President Bush declared a state of emergency last week.
As of Wednesday, McMaster's office has issued 12 subpoenas to question retailers, and Plowden says more subpoenas are possible.
The average price Wednesday for a gallon of regular gas $4.075 in South Carolina, up from $3.522 a month ago and $2.631 a year ago.