All else equal, why are S&P 500 index (SPX) options with lower strike prices more expensive (have higher implied volatilities) than higher strike prices? - Quora
S&P 500 SP500 - Options Chain | ADVFN
SPY Option Chains - Q1 2020 - Q4 2022
S&P 500 Index Options
S&P 500 Index Options - Data Driven Options Trading