An issuer models financial instruments (e.g., proposed securities) with initial financial parameters to facilitate defining a financial instrument with final financial parameters for actual issuance in the primary offering. The issuer models the initial financial parameter data associated with a corresponding proposed financial instrument based on at least market data relevant to the issuance of the proposed financial instrument. The initial financial parameter data is communicated between an issuer and an underwriter in a posting document via a communications network. The issuer and the underwriter collaborate via electronic communications to determine the final financial parameters of a financial instrument to be issued in the primary offering based on the initial parameter data and an agreement between the issuer and the underwriter.