The latest system of national accounts (SNA93) recommended that purchases of software (and any ownaccount production) should be treated as investment as long as the acquisition satisfied conventional asset requirements. This change added about 1 per cent to GDP in most OECD economies in the mid-1990s. However, the range of the revision has been significantly different across countries, leading many observers to question the comparability of these statistics. An OECD task force has formulated a set of recommendations describing a harmonised method for estimating software and this paper provides estimates of changes to GDP levels and growth that might be expected if the OECD recommendations were applied. Estimates of changes are also presented using an alternative harmonised method. Whichever harmonised method is applied, the impact on GDP levels is likely to be significant, and in some countries about 1 per cent of GDP ...