Abstract: A parametric emissions monitoring system for monitoring stationary engine/compressor units coupled to a pipeline provides, in a reciprocating embodiment, reliable and accurate determinations of emission levels for NO.sub.x, CO, and total hydrocarbons (THC) from an emissions matrix primarily as a function of engine speed and engine torque. Validation of the determined emissions level is provided by comparing the values of a set of actual engine operating parameters with a respective value in a set of calculated engine operating parameters to determine whether the deviation of the actual operating parameter from the expected operating parameter is within a defined range, and thus whether the engine is operating within a defined control envelope. Each set of engine operating parameters includes spark ignition timing, fuel rate, and air manifold pressure.