City police are investigating a robbery at the Shell Gas Bar at McNabb & Pine Street.  A male suspect entered the store shortly before 6:30 last night. He jumped on the counter and demanded money.  The male clerk complied with the demand and was not harmed.  The suspect fled the store with a small, undisclosed amount of money.  He is described as approximately 6 feet tall, medium build, 20 to 30 years old.  He was wearing blue jeans and a sky blue jacket with a grey stripe on the sleeves and down the sides.