A number of organisations have provided instructions on how to produce small quantities of liquid oxygen in the classroom using liquid nitrogen and a copper condensation coil (Lister 1995 "Classic Chemistry Demonstrations" (London: Royal Society of Chemistry) pp 61-2, French and Hibbert 2010 "Phys. Educ." 45 221-2). The method presented below describes a process which is believed to be safer as it contains the oxygen during production and produces a controllable amount of the liquid. The method also has the advantage that it can be conducted using cheap and easily available materials.