First, many transporters enjoy a natural or state-granted monopoly and need to be restrained from exercising it with too much abandon.

ECONOMIST: Economics focus

Group-buying is not a natural monopoly, yet there is a limit to how many group-buying websites consumers will use.

FORBES: Online Group Buying's Need For Speed

Further complicating matters, Shell was also negotiating to trade half of its 55% stake in Sakhalin II with state-owned gas monopoly Gazprom for half of a giant natural gas field called Zapolyarnoye.

FORBES: Shell Shocked

The railway involves a natural monopoly: the only other way of getting to the ruins is a four-day hike along the Inca Trail.

ECONOMIST: The battle to reach Machu Picchu

Turkmenistan produces roughly 70 billion cubic metres of natural gas each year and about two-thirds of its exports go to Russia's Gazprom gas monopoly.

BBC: Turkmenistan profile