Marginal cost begins to exceed average cost, creating a profit margin despite competitive pressure to price to marginal cost.

FORBES: Blame Antitrust, Not the Weather, For Travel Woes

Almost every market for technology products or services in China is oversupplied and many firms price below marginal cost.

FORBES: The China Paradox, Part 2: The Trouble With Going Global

All intellectual property violates the efficiency rule that price should equal marginal cost of reproduction, which for knowledge is nearly zero.

ECONOMIST: Non-central Europe

For starters, consider the fact that the degree of market failure varies from region to region: the difference between the price of water and its true marginal cost must be higher in dry places than wet ones.

FORBES: Toilet Training

Time tested economic theory tells us that in a free, unfettered market not constrained by onerous barriers to entry, the long term price of a commodity will approach its marginal cost of production.

FORBES: Gold Sets Up As The Next Great Short

Moreover, CMS chooses as the final price the median among the winning bids, instead of marginal cost, which would drive pricing in a competitive market.

FORBES: The Federal Government's Deeply Flawed System For Controlling Medicare Costs

His conclusion: Disney should charge what the traffic will bear at the gate, then cut the price of individual rides down to their (very low) marginal cost.

FORBES: Magazine Article

As gold declines in price, the least viable mines will be the first closed and bring down the marginal cost.

FORBES: Gold Sets Up As The Next Great Short

"Freemium is really a construct of the digital age because there's almost no marginal cost to digital goods, " said Chris Anderson, author of "Free: The Future of a Radical Price, " and editor in chief of Wired magazine.

WSJ: When Freemium Fails