We use the 1+1 dimensional φ4 and φ6 theory to test the oscillator representation (OR) method. We discuss advantages of the OR method and compare the results with what was already obtained by the method of Gaussian effective potential (GEP). We found that in comparison with the GEP approach, the oscillator representation method allows to discover new vacuum states in the theory. This leads to a correction of the GEP results for the actual vacuum state in some domain of the coupling parameter space. We also discuss the Hartree approximation in φ4 theory comparing with the OR and GEP results.