  To cope with the negative oil futures price caused by the COVID-19 recession,
global commodity futures exchanges switched the option model from Black-Scholes
to Bachelier in April 2020. This study reviews the literature on Bachelier's
pioneering option pricing model and summarizes the practical results on
volatility conversion, risk management, stochastic volatility, and barrier
options pricing to facilitate the model transition. In particular, using the
displaced Black-Scholes model as a model family with the Black-Scholes and
Bachelier models as special cases, we not only connect the two models but also
present a continuous spectrum of model choices.
