HOUSTON, Dec. 7 -- Growing economies and an increasing population would drive up energy demand for decades, despite the world becoming more energy efficient, a U.S. oil expert said here Saturday.

The growth would largely come from emerging economies, where average gross domestic product is expected to grow 2.8 percent annually for years, David Khemakhem, an energy and technology advisor for Exxon Mobil, told an energy conference.

The percentage of households located in urban environments was increasing in emerging economies, which was lifting energy consumption, Khemakhem told the Houston Chronicle.

The number of households in Africa was expected to grow by 70 percent, as the population shifted from larger family structures to more individual family households, thus demanding more energy, Khemakhem said.

He also said India would require more than twice its current level of energy by 2040 due to population growth.

Khemakhem said Asia likely would need to import more than 70 percent of its oil by 2040, up from the current 45 percent. North America, by contrast, had benefited from hydrocarbons discovered in unconventional forms, like shale oil, and was expected to meet its own energy demands by 2040.