Patent pools have many flaws, which may explain why they have been used so infrequently. [http://www.theglobalipcenter.com/sites/default/files/reports/documents/Prizes__Patent_Pools.pdf (GIPC)]
'''Elimination of Competition''' Opponents criticize patent pools for the potential of anti-competitive behavior and collusion, primarily with regards to substitute patents. Substitute patents cover competing technologies that can be developed in parallel without risk of infringement [http://www.wipo.int/export/sites/www/ip-competition/en/studies/patent_pools_report. According to pdf]. Patent pools formed between entitities holding substitute patents eliminates competition in that particular technological sector, reinforcing the World Intellectual Property Organization, "a parallels drawn between patent pool may be regarded as a cartel." pools and cartels [http://www.wipo.int/export/sites/www/ip-competition/en/studies/patent_pools_report.pdf (WIPO)] . Patent pools potentially create a way for companies to share competitively sensitive information, such as pricing, marketing strategies, or R&D information among its members." [http://www.wipo.int/export/sites/www/ip-competition/en/studies/patent_pools_report.pdf (WIPO)]
'''Licensing Practices''' If a patent pool restricts its members from licensing its patents independently, it lowers the incentive to produce alternatives and inflates the costs of goods or technology for consumers. The Department of Justice and Federal Trade Commission state that restrictions on licensing may create "a barrier to entry if existing relationships make it harder for 'new firms to come in and overcome the patent thicket'." [http://www.justice.gov/sites/default/files/atr/legacy/2007/07/11/222655.pdf (DOJ)]