License on a bundle or portfolio of patents, which may be charged at a single royalty rate or based on a royalty formula that does not take account of the number of patents used. Package licenses are often used to license essential technology in patent pools. Where a single royalty rate is charged for the entire package, regardless of the level of use, there is a risk that the arrangement will be regarded as illegal tying under competition and antitrust law, especially where the patents may not be licensed separately and the package includes substitute technologies rather than complementary technologies.