Constrained spectral non-negative matrix factorization (NMF) analysis of perturbed oscillatory process control loop variable data is performed for the isolation of multiple plant-wide oscillatory sources. The technique is described and demonstrated by analyzing data from both simulated and real plant data of a chemical process plant. Results show that the proposed approach can map multiple oscillatory sources onto the most appropriate control loops, and has superior performance in terms of reconstruction accuracy and intuitive understanding compared with spectral independent component analysis (ICA).