The legal requirement of NOx emission reduction from legacy gas engines used in compressor stations asks for an improved engine control. A gas engine is a MIMO system with strong coupling, the inputs and outputs being limited by physical constraints and customer requirements. The engines drive ompressors that change the load at time instants known in advance and the load change pattern can be modeled. A MIMO online linear model predictive controller (MPC) with the objective of keeping the fuel/air ratio and the engine speed constant was applied and compared to the standard SISO PID controls. The tracking of the fuel/air ratio during the transients was improved up to 80% when using the MPC approach which is sufficient to meet the up-coming emission legislation.