A local volatility model, in mathematical finance and financial engineering, is an option pricing model that treats volatility as a function of both the current asset level S t {\displaystyle S_{t}} and of time t {\displaystyle t} . As such, it is a generalisation of the Black–Scholes model, where the volatility is a constant (i.e. a trivial function of S t {\displaystyle S_{t}} and t {\displaystyle t} ). Local volatility models are often compared with stochastic volatility models, where the instantaneous volatility is not just a function of the asset level S t {\displaystyle S_{t}} but depends also on a new "global" randomness coming from an additional random component.