The paper deals with the problem of argumentation literacy in the field of university ESP teaching. It presents the analysis of arguments that university students put forward while writing argumentative essays as part of their final English tests. The analysis concerns essays written by students at various levels of command of English, namely B2 and C1 levels. The analysis is aimed at showing connection between students' language ability and their argumentative ability. The findings obtained stress the necessity to develop in ESP students argumentative literacy, that can be considered as one of the main soft skills needed in all spheres of professional and academic life.