Otto cycle is also known as constant volume cycle, as the heat is received and rejected at a constant volume. Otto cycle is used in gas, petrol and many of the oil engines. Otto cycle is a thermodynamic cycle on which the petrol engine works.

The ideal Otto cycle consists of two constant volume and two reversible adiabatic or isentropic processes.

Otto cycle is taken as a standard of comparison for internal combustion engines. For the purpose of comparison with other cycles, the air is assumed to be the working substance.