The basic form of economic exchange is a bilateral relationship between buyer and seller. If economic conditions are common knowledge there is no problem in principle to determine the efficient quantity to trade. But if benefits are known only to the buyer and costs are known only to the seller...

This paper studies the efficient agreements about the dependence of workers' earnings on employment, when the employment level is controlled by firms. Under plausible assumptions, such agreements will cause employment to diverge from efficiency as a byproduct of their attempt to mitigate risk....