How has online retail giant Amazon become so profitable?

Amazon shares have surged more than 18% in after-hours trading after it reported a surprise profit and better-than-expected sales figures.

The online retail giant reported a $92m profit compared to a $126m loss for the same period a year ago.

Sales also rose 20% to $23.2bn in the second quarter to the end of June, boosted by strong growth in the US.

Its shares, which fell 1.3% during the day, leapt 18.5% to $571.24 a share in after-hours trading on Wall Street.

Michelle Fleury explains how the company has become so profitable.