The Great Western Railway (GWR) 3100 Class was a class of 2-6-2T side tank steam locomotive.

This class of large prairie was created in 1938 when Collett rebuilt some of Churchward's 3150 Class with a view to using them as bankers, particularly from Severn Tunnel Junction shed. These engines used the standard class 4 boiler again, but pressed to 225 psi (1,550 kPa). and using smaller coupled wheels of 5 feet 3 inches (1.600 m) diameter, and one-half inch (13 mm) increase in cylinder diameter, nominal tractive effort rose to 31,170 pounds (14,140 kg). Almost impossible to pick out was a 2 in (50.8 mm) reduction in pony truck wheel diameter to 3 ft 0 in (914 mm). Only five engines were ever modified, namely 3173, 3156, 3181, 3155 and 3179 which were rebuilt as 3100 to 3104 respectively. None of these were preserved.

• GWR 3100/5100 Class (1906)
• GWR 3150 Class
• GWR 5101 Class
• GWR 6100 Class
• GWR 8100 Class
• List of GWR standard classes with two outside cylinders

• Whitehurst, Brian (1973). Great Western Engines, Names, Numbers, Types and Classes (1940 to Preservation). Oxford, UK: Oxford Publishing Company. pp. 30, 102, 135. ISBN 978-0-9028-8821-0. OCLC 815661.

• Class 3100 Details at Rail UK