This paper examines earnings differences between first-generation and continuing generation college graduates across 24 OECD countries using data from the OECD Survey of Adult Skills (PIAAC). In all but two of the countries analysed, first-generation graduates earn less than their peers from college-educated families, with an average gap across all countries of approximately 8%. We investigate potential mechanisms behind this result and find that first-generation graduates are less likely to pursue postgraduate education, more likely to hold vocational degrees, and tend to have lower cognitive skills. These findings highlight the need for policy interventions to enhance educational mobility and promote equality of opportunity.