Unlike stocks and shares, the majority of transactions in the philatelic or stamp market take place informally, by mail order, or in retail environments, and therefore the size of the market is hard to determine. The market is certainly much smaller than the financial markets but it is not trivial. It has been estimated at £5 Billion. The majority of these transactions, however, are likely to be low value items rather than investments. In a 2007 it was estimated that about $1 billion of rare stamps trade annually in the $10 billion-a-year stamp market. The number of collectors worldwide was estimated at 30 million in 2004.