 When World War II threatened tropical sources of natural latex for rubber , Sarnia was selected as the site to spearhead development of synthetic petroleum @-@ based rubbers for war materials , and Polymer Corporation was built by Dow Chemical at the request of the Government of Canada . Large <unk> bring Alberta oil to Sarnia , where oil refining and petrochemical production have become <unk> of the city 's economy . Shell Canada , Imperial Oil , and <unk> Energy ( <unk> ) operate refineries in Sarnia . Large salt beds found under the city became a source of chlorine and other significant ingredients which contributed to the success of Chemical Valley . Chemical companies operating in Sarnia include <unk> Chemicals , Bayer ( Lanxess and <unk> <unk> ) , <unk> Corporation and <unk> Corporation . 
