This article explores what factors determine the decision of a patent pool to accept new inputs. Thereby we are able to test directly the allegations that pools allow some firms to include strategic patents and thereby to increase their share in the royalty income. We propose a dynamic analysis of 1337 U.S. patent inputs into 7 important pools. This analysis highlights a trade-off between firm and patent characteristics. For instance we prove that firms already member of the pool are able to include lower quality patents. This finding can be explained both by bargaining power and information asymmetry. Further analysis confirms that the insiders’ information advantage plays an important role. In particular, as measured by a new indicator, pool members and firms practicing the technology file patents that are better aligned with the criteria of essentiality.