VATICAN CITY (AP) — Pope Francis has told world oil executives that the transition to less-polluting energy sources "is a challenge of epochal proportions."

Francis told the gathering Saturday that modern society with its "massive movement of information, persons and things requires an immense supply of energy." And still, he said, as many as one billion people lack electricity.

The pope said that meeting the energy needs of everyone on Earth must be done in ways "that avoid creating environmental imbalances resulting in deterioration and pollution gravely harmful to our human family, both now and in the future."

The Vatican says the two-day conference with oil executives that ends Saturday is a follow-up to the pope's encyclical three years ago calling on people to save the planet from climate change and other environmental ills.