We examine why cooperation among essential patent holders may not occur, despite significant gains for them and the users. We use the sequential coalition formation framework to show that no coalition may form when the number of patent holders is large, if a firm initiating the coalition can negotiate only sequentially and individually with the rest. Our results, complementing Ray and Vohra (1999) suggest that voluntary sequential negotiation cannot prevent the emergence of "tragedy of anticommons", even if side payments are allowed.