It really depends on your country and on the demography. This answer requires strong social science research and, to my knowledge there are only a few studies on PhDs employment rate, mainly in America and EU.
The Atlantic published an article in 2014 following the unemployment of PhDs in USA..In the image below you can see unemployment rate distributed among the different areas of study.
Nevertheless, I think the unemployment rates are not only influenced by the field of study but they are also related with:
a) The fast growing of PhD holders and the lack of professor jobs in the Academia.
b) The lack of transferable skills training, and the lack of career support in the Universities Graduate Programs. These skills are essential for the transition of PhD holders to jobs outside academia.