This study examines the factors that shape secondary schools' offerings of academic curricula. While academic curricula provide many benefits to individuals and the larger society, inequalities in opportunities to study these subjects may exist between schools, even in comprehensive secondary education systems. We examine the Australian case as a vehicle for developing a theoretical framework about the causes of stratified and unequal access to academic curricula in comprehensive secondary education systems. We interviewed 17 school leaders from a range of secondary schools about their curricular offerings. All school leaders reported that curricular offerings are based on student choice and that subjects with sufficient demand are financially sustainable. But regardless of student choices, some schools offered academic curricula to maintain their reputation and competitive advantage in the education marketplace. School leaders of low socioeconomic public schools reported the most resource constraints in offering academic curricula, and all school leaders acknowledged systemic constraints related to the large number of curricula that could be offered. The findings highlight how marketisation dynamics combine with curriculum policies to shape schools' curricular offerings in ways that provide unequal access for different types of students.