Thus a riskless profit (after commissions) is made. However, in fairly efficient markets, price differentials are so small that arbitrage strategies do not guarantee profits because of the very low...

Thus a riskless profit (after commissions) is made. However, in fairly efficient markets, price differentials are so small that arbitrage strategies do not guarantee profits because of the very low profit margins. Sometimes such trading is impractical or not feasible because of the large asset quantities one must trade to obtain some profit.