The marginal revenue curve reflects the degree of market control held by a firm. For a perfectly competitive firm, the marginal revenue curve is a horizontal, or perfectly elastic, line. For a monopoly, oligopoly, or monopolistically competitive firm, the marginal revenue curve is negatively sloped and lies below the average revenue (demand) curve.

Marginal Revenue Curve, Perfect Competition

Marginal revenue is commonly represented by a marginal revenue curve, such as the one labeled MR and displayed in the exhibit to the right. This particular marginal revenue curve is that for zucchini sales by Phil the zucchini grower, a presumed perfectly competitive firm.

The vertical axis measures marginal revenue and the horizontal axis measures the quantity of output (pounds of zucchinis). Although quantity on this particular graph stops at 10 pounds of zucchinis, the nature of perfect competition indicates it could easily go higher.

This curve indicates that if Phil sells the first pound of zucchinis (an increase in production from 0 to 1), then his extra revenue is $4. However, if he sells his tenth pound (an increase in production from 9 to 10), then he also receives $4 of extra revenue. Should he sell his hundredth pound (an increase in production from 99 to 100), then he moves well beyond the graph, but his marginal revenue remains at $4.