Intra-day volatility

FX trading is centered around a handful of currency pairs referred to colloquially as the big seven. The high volume and liquidity combined with fewer active instruments generates greater intra-day volatility than the equity markets where hundreds of stocks are actively traded. It is this volatility that can be profitability exploited by forex traders.

Low spreads
Currency trading offers spreads that are much lower than what can be obtained when buying or selling equities, especially during after-hours trading. Although exceptionally tight currency spreads were previously reserved for transactions involving $1 million or more, a shift towards tighter spreads for smaller transactions is gaining traction. Again, OANDA's FXTrade is an industry leader in offering tight spreads regardless of the size of the trade.

Margin-based leverage
Leverage—or margin based trading—makes it possible for FX market participants to submit trades valued considerably higher than the deposits in their trading accounts. Typically, margin ratios for trading currencies are higher than those permitted for equities, and this is primarily attributable to the higher level of liquidity within the currency markets.
To illustrate the power of leverage provided through the use of margin, consider a margin ratio of 20:1 coupled with a trading account containing $10,000. This means that you could trade amounts up to $200,000! Trading in larger volumes allows you to take better advantage of even small price movements (but can also dramatically increases your risk). Read about OANDA's margin policy.