There are many examples of markets where an agent who wants to get out of an investment position quickly may find himself trapped and forced to remain in that position because of a lack of liquidity. What are the asset-pricing implications when agents cannot always buy and sell assets...

We investigate the properties of mean-variance efficient portfolios when the number of assets is large. We show analytically and empirically that the proportion of assets held short converges to 50% as the number of assets grows, and the investment proportions are extreme, with several assets...