On a global scale, calculating the amount of waste being generated presents a problem. There are a number of issues, including a lack of reporting by many countries and inconsistencies in the way countries report (definitions and surveying methods employed by countries vary considerably). The Basel Convention has estimated the amount of hazardous and other waste generated for 2000 and 2001 at 318 and 338 millions tonnes respectively. These figures are based on incomplete reports from the parties to the Convention. Compare this with the almost 4 billion tonnes estimated by the OECD as generated by their 25 member countries in 2001 (Environmental Outlook, OECD) and the problems of calculating a definitive number for global waste generation are obvious. Therefore the figures shown below should be used with caution.