How much would an outside second Ph.D. supervisor get paid in the U.S.? I have been asked to consider being a second supervisor on a Ph.D. project for a doctoral candidate at a U.S. university. As I am in the Netherlands, this does not fall under my normal employment. Does anyone know where I might find information about the normal fee for this type of supervision?

Thanks in advance for any assistance.
As far as I know nothing.

I've never heard of outside supervisors (in industry or academia) ever getting paid anything.

You should talk to your employer, if he is willing to donate some of your time for this supervision. (Depending on the research being done, there may also be some benefit for him.)