Waves of gleaners sift the sweepings of Hanoi's streets, just as children pick over the rubbish of Maputo's main tip.

ECONOMIST: Bursting cities, bust infrastructure

Like biblical gleaners extracting more wheat from long-tilled acreage, Duroc-Danner is revitalizing oil flows from aging fields once thought to be largely tapped out.

FORBES: Oil Gleaners