In several OECD countries, investment rates in the business sector grew strongly in the second half of the 1990s. In some cases, the strength of private investment relative to output growth had raised concerns about the risk of capital overhang and the prospect of a prolonged period of slow capital formation in order to bring investment levels back to more sustainable levels. It is possible that the stock market boom has contributed to a rise of investment demand to an excessive level, not only in the United States, but also in the United Kingdom, Canada, Scandinavia and Greece. The purpose of this paper is to assess the contribution of fundamental determinants to the change in investment in the second half of the 1990s, based on the estimation of panel cointegration equations for gross business investment for 18 OECD countries from 1970 to 1999. In addition to the levels of real GDP and a measure of the cost of capital, the set of explanatory variables includes four alternative ...