General Electric's BWR product line of boiling water reactors represents the designs of a relatively large (~18%) percentage of the commercial fission reactors around the world. The progenitor of the BWR line was the 5 MW Vallecitos Boiling Water Reactor (VBWR), brought online in October 1957. Six design iterations, BWR-1 through BWR-6, were introduced between 1955 and 1972. This was followed by the Advanced Boiling Water Reactor (ABWR) introduced in the 1990s and the Economic Simplified Boiling Water Reactor (ESBWR) introduced in the early 2010s.