James Petras is not simply a "liberal". He is an avowed Marxist.

James Petras, a retired Bartle Professor (Emeritus) of Sociology at Binghamton University, SUNY, New York, USA, and adjunct professor at Saint Mary's University, Halifax, Nova Scotia,Canada. He describes himself as a "revolutionary and anti-imperialist" activist and writer.
James Petras - Wikipedia, the free encyclopedia

A google search of his name turns up numerous articles pointing to his erroneous facts and figures, as well as others that refute his positions.