The new stations will be installed in Davis, Powder House, Ball, and Wilson/Porter Squares, the city said.
Current stations are located at Conway Park at Somerville Avenue, City Hall, Union Square, and Beacon Street at Washington Street.
The city and Hubway have agreed to install another four stations in Somerville, but the locations are still up in the air, said Thomas Champion, spokesman for the city.
"The commitment is to do another four," Champion said. "But where exactly those will go will be determined by how the eight get used."
Matt Byrne can be reached at email@example.com.