Spectrum leasing from a primary user to a set of secondary users may be implemented by requiring the secondary nodes to pay back the primary for the leased spectrum via cooperation (relaying). In this paper, this principle is studied from an information-theoretic standpoint by focusing on a scenario with one primary node and multiple secondary nodes, which may act as relays for the primary, communicating to a common receiver. The scenario is modelled as a multirelay channel where each relay (secondary user) has a private message for the destination. Achievable rate regions are derived for discrete memoryless and Gaussian models by considering Decode-and-Forward (DF), with both standard and parity-forwarding techniques, and Compress-and-Forward (CF), along with superposition coding at the secondary nodes. Numerical results for the Gaussian channel confirm that spectrum leasing via secondary cooperation is a promising framework to enable secondary spectrum access.