This article is concerned with the source of men's invisible advantage in the male-dominated disciplines of Science, Technology, Engineering and Mathematics (STEM). It is suggested that this advantage has been obscured by combining sponsorship and mentoring. The research asks: Are men or women most likely to be mentored? Is it possible to distinguish between mentoring and sponsorship? Is there gender variation in either or both of these depending on the source -- whether from the academic supervisor, line manager or other senior academics? This qualitative study draws on interview data from 106 respondents (57 men and 48 women) at high, mid and early levels, in four universities: one each in Bulgaria, Denmark, Ireland, and Turkey. It shows that both men and women received mentoring from their PhD supervisor, albeit with slightly different reported nuances. Men were more likely than women to receive sponsorship in that relationship. Both men and women received sponsorship from the Head of Department, whose wider responsibilities may have reduced homophily. Men were more likely than women to receive sponsorship and mentoring from senior men, with most women indicating a lack of access to such senior academics. By distinguishing between mentoring and sponsorship, this article contributes to our understanding of the way male dominance in STEM is perpetuated and suggests the source of men's invisible advantage in STEM.