The long-term planning problem for integrated gas field development is investigated. The key decisions involve both design of the production and transportation network structure and operation of the gas fields over time. A novel continuous-time modeling and optimization approach is proposed, which introduces the concept of event points and allows the well platforms to come online at potentially any time within the continuous horizon under consideration. A two-level formulation and solution framework is developed to take into account complicated economic calculations and results in mixed-integer nonlinear programming (MINLP) problems. As compared with the discrete-time model, the proposed approach leads to more compact mathematical models and significant reduction of the size of the resulting MINLP problems. Even though, the proposed approach in its current form cannot guarantee convergence to the optimal solution, computational results show that this approach can reduce the computational efforts required substantially and solve problems that are intractable for the discrete-time model.