The efficiency of an underground coal gasification (UCG) energy conversion process can be increased by maintaining a desired heating value of the product gases. In literature this task has been accomplished by adopting nonlinear model-based control strategies. To exploit the flexibility of the linear control design techniques, a linear model of the UCG process has been developed, which retains the dynamics of the nonlinear model around the operating point of interest. To account for external disturbance and modelling inaccuracies, an output-based robust multi-objective H-2/H-infinity control law integrated with pole placement has been proposed. The problem is solved by formulating linear matrix inequality (LMI) constraints for performance and robustness. The simulation results show that the designed controller gives adequate performance in the presence of modelling inaccuracies and external disturbance. Moreover, it has been shown that performance of the designed controller is better as compared to the standard PI controller.