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Compare that to the £40bn-45bn that the entire annual global market is thought to be worth at the moment and it shows just how much is at stake at the top end of art auctions.

The continuing boom is driven pre-eminently by the Impressionist, Modern, Post-War and Contemporary art sectors. Christie's recent London and New York sales in this sector accounted for almost two-thirds of their entire auction total for the first six months.

As well as those sectors, the areas of stiffest competition between the two rivals can be found in the Asian market and the development of their private sales divisions and online offers.

Add the private sales to their auction totals and Christie's posted $4.47bn (£2.73bn) for January to June, citing an increase in the value of artworks across the major categories, far greater online activity and the growing influence of new buyers. New clients represented 24% of all buyers and 15% of the sales total in the first half of 2014, they said.

Sotheby's also stressed the importance of new buyers: 26% of all their buyers in the first half of 2014 were new to them and they aim to grow this figure exponentially via a new partnership with eBay, announced just before they released their results. More on this in next week's issue.

Private Sales

Private sales contributed $828.2m (£506m) at Christie's, who are due to extend their facilities in New York in the autumn to expand this side of the business. Sotheby's have yet to release their private sales figures, but they are likely to make as major a contribution to the bottom line as that of their rivals.

A variety of statistics are available for online performance. The number of lots purchased online in 2013 increased by 36% at Sotheby's, where mobile traffic now accounts for 25% of Sotheby's total website traffic. Meanwhile, the first half of 2014 saw 2.3 million visits to christies.com from mobile devices, accounting for 20% of all website traffic.

Exact comparisons are not easy, but it is clear that while developing client relationships remains at the core of business at the top end, the real revolution is in attracting new buyers via the web.

Sotheby's were keen to highlight a dip in Christie's sales in Asia, while the latter pointed to their new Shanghai premises, due to open in October, as evidence of their increasing influence in the region.