APA

Roorda J., Shell, World Petroleum Congress (10th : 1979 sept. 9-14 : Bucharest) & Shell.Petroleum in world energy balances to the year 2000. : .

Chicago

Roorda John, Shell, World Petroleum Congress (10th : 1979 sept. 9-14 : Bucharest) and Shell.Petroleum in world energy balances to the year 2000. : .

Harvard

Roorda J., Shell, World Petroleum Congress (10th : 1979 sept. 9-14 : Bucharest) and Shell.Petroleum in world energy balances to the year 2000. : .

MLA

Roorda John, Shell, World Petroleum Congress (10th : 1979 sept. 9-14 : Bucharest) and Shell.: . .