Foreign exchange trading increased by 38% between April 2005 and April 2006 and has more than doubled since 2001. This is largely due to the growing importance of foreign exchange as an asset class and an increase in fund management assets, particularly of hedge funds and pension funds. The diverse selection of execution venues such as retail trading platforms platforms offered by companies such as ParagonEX, First Prudential Markets and Saxo Bank have made it easier for retail traders to trade in the foreign exchange market. In 2006, retail traders constituted over 2% of the whole FX market volumes with an average daily trade volume of over US$50-60 billion (see retail trading platforms).[5] Because foreign exchange is an OTC market where brokers/dealers negotiate directly with one another, there is no central exchange or clearing house. The biggest geographic trading centre is the UK, primarily London, which according to IFSL estimates has increased its share of global turnover in traditional transactions from 31.3% in April 2004 to 34.1% in April 2007. The ten most active traders account for almost 80% of trading volume, according to the 2008 Euromoney FX survey.[3] These large international banks continually provide the market with both bid (buy) and ask (sell) prices. The bid/ask spread is the difference between the price at which a bank or market maker will sell ("ask", or "offer") and the price at which a market-maker will buy ("bid") from a wholesale customer. This spread is minimal for actively traded pairs of currencies, usually 0–3 pips. For example, the bid/ask quote of EUR/USD might be 1.2200/1.2203 on a retail broker. Minimum trading size for most deals is usually 100,000 units of base currency, which is a standard "lot".