1.		Ninth World Energy Conference : the economic and environmental challenges of future energy requirement. population and energy resources / Ninth World Energy Conference
2.		Ninth World Energy Conference: the economic and environmental challenges of future energy requirements: environment and the energy supply / Ninth World Energy Conference
3.		Ninth World Energy Conference: the economic and environmental challenges of future energy requirements: energy resource recovery / Ninth World Energy Conference
4.		Ninth World Energy Conference: the economic and environmental challenges of future energy requirements: energy conversion / Ninth World Energy Conference
5.		Ninth World Energy Conference: the economic and environmental challenges of future energy requirements: transportation of energy / Ninth World Energy Conference
6.		Ninth World Energy Conference: the economic and environmental challenges of future energy requirements: utilization of energy / Ninth World Energy Conference