Similar to the standard geometry optimization, MECIs can be located with analytic derivatives. Recent studies on CASPT2 have enabled the exploration of CI regions using analytic derivative coupling vectors at the XMS-CASPT2 level of theory. Non-adiabatic MD simulations can be performed as well. GVVPT2 16 may also be used to explore CIs, and a formulation for derivative coupling vectors exists; 48 however, an actual implementation has not been achieved so far. NEVPT2, MCQDPT2, and SA-DSRG-MRPT2 29 can also be used for MECI search, while MC-PDFT has been used for studying intersystem crossings. Although OpenMolcas is the program package with the original implementation of CASPT2, its analytic gradient has not been developed for 30 years. Recently, one of the authors has succeeded in this task for the single-state version of CASPT2. However, the code for the multistate extension is not yet available. Furthermore, it would be interesting to see how the new XDW-CASPT2 and RMS-CASPT2 approaches perform in MECI searches. In this study, we outline the analytic derivative theory for (X)MS-, XDW-, and RMS-CASPT2, as well as their RASPT2 extension. The developed method is used to locate minimum energy structures and MECIs of typical systems, and the smoothness of PESs around MECIs, as well as their dependence on the different flavors of CASPT2/RASPT2, are discussed to evaluate the applicability of these methods.