<p>Part-time work remains largely feminized in Spain. Contrary to the common belief that women primarily engage in part-time work due to caregiving responsibilities, our findings reveal that half of these workers would prefer full-time positions. This indicates that part-time employment is mostly undertaken on an involuntary basis. Drawing on new survey data, we adopt a revealed-preferences approach and find that women do not exhibit a stronger aversion to longer working hours than men, challenging the idea that part-time jobs respond to labor market supply, rather than demand. Total wages and non-monetary job benefits, which are less prevalent in part-time jobs, are found to be particularly relevant in shaping job satisfaction. Further analysis of Labor Force Survey data identifies sectoral and, more importantly, occupational segregation as the major factor behind the gender gap in part-time employment: the gap is halved when comparing men and women within the occupation and sector and narrows further when focusing on involuntary part-time work. These findings highlight the central role of segregation in this enduring gap and underscore the necessity of targeted policy interventions.</p>