Founded in 1952, Products Tank Line (renamed Procor in 1962) constructed their manufacturing plant in the mid 1950's in Oakville, Ontario. Initially, engineering was supplied by parent Union Tank Car Company. In the 1960's, Procor assembled their own engineering department and crafted a series of standard design tank cars which paved the way for a new generation of equipment, with many modern designs reflecting this new standard. The GP20 (the tank car, not the locomotive) was suitable for lighter density commodities which would not congeal or freeze in cold weather, such as various oils and fuel. The same car could also be equipped with interior heater coil pipes, such that the contents could be reheated. The same basic design - including tank diameter and length - was manufactured from 1969 through until 1984. The GP20 was constructed with both 70 ton and 100 ton capacity trucks. Later designs were also equipped with a separate fittings dome (in addition to the manway assembly fitting), which allowed the tank rating to be upgraded from 60 psi to 100 psi.
Reference: Rapido Trains