A rotary pulser for transmitting information in a mud pulse telemetry system of a drilling operation. The pulser has two rotors mounted adjacent each other so that obstruction of the passages formed between the blades in one pulser by the blades of the other pulser creates pressure pulses in the drilling fluid. Each rotor is separately controlled and can be rotated continuously in one direction or oscillated. The ability to rotate each rotor separately provides flexibility in the pulser's operating mode, so as to allow more efficient generation of pulses, and also enhances the ability of the pulser to clear debris that would otherwise jam or obstruct the pulser.