When Papua New Guinea joined the ranks of the world’s significant energy exporters four years ago, the government was betting on a revenue windfall it hoped would transform the impoverished South Pacific nation better-known for jungles, violence and corruption.
But the payday from a $19 billion Exxon Mobil Corp.-led natural-gas project has so far been a trickle, crimped by a downturn in gas prices that allowed Exxon and its partners to claim losses against royalty payments. A 7.5-magnitude earthquake in February that killed...