Some effort has been done in evaluating the price of patents. The company Ocean Tomo is quite far in providing (allegedly) rather accurate prise evaluations of single patents and patent portfolios. According to J. Malackowski, founder of Ocean Tomo, basically three ways of evaluation appear to be practised :
1) cost base approach
2) market value approach
3) Income approach
Well, let's have a more profound look on these three approaches in the light of the data available:
Cost base approach
From a study done by Gasnier, an evaluation of the out of pocket expenditure, including both patent attorney fees and official fees, for obtaining patent protection in the United States, Japan and three major European states (DE, FR and EN) is estimated to be on average per patent family :
From these data, a 10 year old patent family would on average be worth 80 k€, whereas a 3 year old patent family would on average be worth 10k€.
Market value approach
From data gathered from published results of auctions held by Ocean Tomo, a average selling price can be deduced .
From the data between 2006 and 2011, an average sales price of 106 k€ can be calculated, with extremes (in the average sales price) varying between 25k€ and 300k€. This price is based on the sales of about 980 patent families, wherein the day to day Dollar/Euro rate of exchange has been applied. The four auction average (green line) shows a slightly declining tendency. It is remarked that the data of last ICAP/Ocean Tomo auction of March 30/31, 2011 were not taken into account, since at this auction, for the first time ever, covenants not to sue were offered, of which at least one was sold for a stunning 35 million $ (35E6$). These covenants however are blurring the sales price figures of patents as such. Furthermore, after the takeover of ICAP of the IP auctions of Ocean Tomo, auction results are less and less published, which will render it more difficult in the future to obtain valuable data on market based patent price indications.
Remarkably, an auction held by IP Auctions GmbH (for obvious reasons, now out of business) in Munich in May 2007, resulted in an average sales price of patents sold of less than 6 k€, based on 83 offered families . This means that patents sold in Europe are on average selling for a factor 18 less than the average price in the US. When compared with the average cost base evaluated price, selling patents in Europe is not quite a profitable business.
Income based approach
In a study performed on assignment by the European Union, based upon about 10 000 questionairs, handed out to inventors and patent holders, representing about the same number of patent families another picture emerges :
Leading to an average value of approximately 3 million Euro [3E6€], a remarkable 30 times more that the average sales price in the US market and, even more stunning, a 500 (!) times more than the average auction sales price in Europe.
Conclusion and discussion
In a cost based approach, inevitably, older patents are valuated more expensively, since more costs have arisen. In this model, the older the patent, the more expensive it is going to be, whereas less and less time remains for exploiting it. In itself, the cost base approach can thus be seen as quite a questionable model.
In an income based approach, the value of patents appear quite overestimated by patent holders themselves. This price evaluation model carries along some inevitable crystal ball, hope for income effects, rendering a price evaluation of EP patents on average a factor 500 higher than the prices actually paid for on auction in Europe.
It is my firm believe that the difference in average sales prices of patents between auctions held in Europe and auctions held in the US of a factor 18 is due to the complex and inefficient European patent system, when compared with the straight forward single market, single economy US patent system.
One can arguably say, that due to the relative complex and burdensome patent enforcement in Europe and relative expensive European patent system, patent applicants first have to pay 10-20 times more money, to obtain a patent worth 18 times less than a US patent . A unification of the European patent litigation system will thus be likely to both decrease the costs and increase the value, rendering patenting trading business in Europe a stunning factor 250 more profitable. The patent trading (by some denounced patent trolling) in Europe will instantaneously emerge, as soon as the patent system is finally unified.
The slow European political systems -it is now 36 years after the first community patent convention (CPC) has been drafted - and above all the unification blocking of patent wise unimportant countries such as Italy and Spain are costing (predominantly European) enterprises considerable amounts of money. Even if a new CPC will finally be agreed upon, it will last some more years to be finally ratified and to enter into force.
From the above given data, the best evaluation of a patent appears to be the market value approach. By trying to find similar patents and to search for their sales prices, an appropriate value may be evaluated.
For evident reasons, however, the prices of patents, sold at auctions are less and less easy to be found on the web. The companies providing price evaluations, more and more keeps commercial auction data undisclosed, such that others, including patent holders can no longer make a fairly accurate marked price evaluation themselves and more firmly depend on them.
So the best evaluation method available is likely to disappear, which, I believe, is on the long term neither in the interest of the companies organising the auctions and providing valuations nor in the interest of the other stakeholders.
It is my prediction that in this market, like in every fully grown market, in the future open bidding and price forming systems will appear, leading to a transparent system, where patent valuation can be a relative straight forward exercise, based upon a market approach model. The unification of the European system will contribute to such transparant system and will strongly accelerate its process of development.
Till that time, patent evaluation remains inevitably a partially crystal ball and gut feeling business.
 S. Graj, "The IP quake Behind how You Bet Your Asset", Interview J. Malackowski (15-05-2011), http://www.ggny.com/blog_gg/?p=732
 A. Gasnier, "The Patenting Paradox" (2008), p. 88-89.
 Ocean Tomo and ICAP information on auctions (2006-2011), (most auction results are no longer available).
 J. Ostler, "IP Auctions GmbH first sale of patents at live auction in Munich" (2007), http://www.drs-digital.com/dataroomservices-news-events-2-10/archive/2007-en/ip-auctions-sales-patents.html
 A. Gambardella e.a., "The Value of European Patents" (2005), http://www.ulrichkaiser.com/patval/Final_Report_PATVAL.pdf
 A Single Market for Intellectual Property Rights, Boosting creativity and innovation to provide economic growth, high quality jobs and first class products and services in Europe (25-05-2011), http://ec.europa.eu/internal_market/copyright/docs/ipr_strategy/COM_2011_287_en.pdf
 M.Hoffmann, "The EU ‘Community Patent’ – a new, better patent protection regime?", News Link, (spring 2004), http://www.worldlink-law.com/pdf/newslink_spring04.pdf