In this work we have implemented the σ p regularization technique in CASPT2. The resulting methodology, σ p -CASPT2, compares favorably to previous approaches based on the real and imaginary level shifts in terms of its efficacy in removing the intruder state problem and the sensitivity of the results with respect to the input parameter. It was found that the two variants considered, σ 1 -CASPT2 and σ 2 -CASPT2, are suited for different use-case scenarios.