I will describe our study of singlet oxygen photochemically generated at a water-solid interface, and how ¹O₂ then diffuses into the aqueous medium. Collaborations with Ruomei Gao and Harry Gafney revealed that singlet oxygen is generated cleanly in aqueous solution upon irradiation of a heterogeneous complex, meso-tetra(N-methyl-4-pyridyl)porphine adsorbed onto porous Vycor glass (PVG). Despite the effectiveness of this and other heterogeneous systems to generate ¹O₂, little is known about the dynamics of O₂ quenching at water-solid interfaces. For example, how does the oxygen encounter the excited heterogeneous sensitizer? What mechanism (static or dynamic) converts ground-state oxygen into singlet oxygen, which then escapes into the surrounding aqueous solution? Our recent work with Jovan Giaimuccio and Jerry Meyer led us to conclude that O₂ quenching at the glass-water interface differs from O₂ quenching at the glass-gas interface. Sensitizer binding and distribution, and excitation intensity distribution within the porous glass are examined in the hopes of optimizing ¹O₂ formation and diffusion into the surrounding aqueous environment.