▁H BO G ▁expanded ▁during ▁the ▁ 1 9 4 0 s ▁and ▁ 5 0 s , ▁and ▁in ▁ 1 9 6 0 ▁began ▁sh ipping ▁Canadian ▁cru de ▁to ▁a ▁ref in ery ▁in ▁Bill ings , ▁Mont ana ▁through ▁a ▁new ▁link ▁to ▁the ▁Gla cier ▁pipeline . ▁The ▁company ▁became ▁the ▁sixth - larg est ▁Canadian ▁producer ▁in ▁ 1 9 6 7 . ▁In ▁ 1 9 7 3 , ▁H BO G ▁acquired ▁ 3 5 % ▁st ake ▁in ▁Sie b ens ▁O il ▁and ▁Gas , ▁but ▁by ▁ 1 9 7 9 ▁it ▁div ested ▁its ▁interest . ▁ ▁In ▁ 1 9 8 0 , ▁H BO G ▁bought ▁a ▁cont rolling ▁interest ▁in ▁Ro xy ▁Pet role um . ▁In ▁the ▁ 1 9 8 0 s , ▁sales ▁and ▁oil ▁prices ▁sli pped , ▁while ▁deb t ▁from ▁ac quis itions ▁p iled ▁up ▁which ▁led ▁Hudson ' s ▁Bay ▁Company ▁to ▁sell ▁off ▁its ▁ 5 2 . 9 % ▁st ake ▁in ▁H BO G ▁to ▁D ome ▁Pet role um . ▁However , ▁as ▁a ▁result ▁of ▁the ▁ 1 9 8 6 ▁drop ▁in ▁world ▁oil ▁prices ▁and ▁substantial ▁deb ts ▁from ▁past ▁take o vers , ▁D ome ▁Pet role um ▁became ▁an ▁ac quisition ▁target . ▁In ▁November ▁ 1 9 8 7 , ▁after ▁months ▁of ▁neg ot iation , ▁an ▁agreement ▁in ▁principle ▁was ▁reached ▁with ▁Am oco ▁Canada ▁Pet role um