A geometric representation of the economic loss of welfare caused by market failure or government failure. On a price-quantity diagram, with price on the vertical axis and quantity along the horizontal axis, the efficient equilibrium, characterized by price p* and quantity q* is at the point where the curves representing the marginal social benefit (MSB) and the marginal social cost (MSC) of an economic activity intersect. An equilibrium at a different quantity, q₀, is characterized by deadweight loss measured by the area of the Harberger triangle, with vertices at the efficient equilibrium and the points of intersection of the vertical line at q₀ with the MSB and the MSC curves. In the analysis of a monopoly, the relevant MSB curve is the market demand, the MSC curve is the marginal cost curve of the monopolistic producer, and q₀ is the monopolistic profit-maximizing quantity. In the analysis of a distortionary consumption tax the MSB and the MSC curves are the demand and supply curves without tax, and q₀ is the equilibrium quantity in the presence of tax. In the latter case, a simplified approach uses Marshallian demand; Harberger proposed to use the demand resulting after the lump-sum rebate of tax revenue to the consumers, sometimes called the Harbergerian demand; Hicksian demand, compensating variation, and equivalent variation are also commonly used, producing different but largely comparable estimates of the size of the loss.