Inverted skew for options on commodities

Options on equities are well-known to exhibit "volatility skew", meaning the volatility of option goes down as the strike price goes up. This is because, at least partly, as the stock price moves up, there is less perceived chance of going even higher, whereas when it moves down, the chance of falling further often increases, at least partly, due to the "fear factor". Put it simply, the price going up in equity markets generaly means the perceived performances of underlying corporate are good.

On the other hand, the opposite can be said for commodities. Options on commodities tend to exhibit "inverted volatility skew", meaning the volatility goes up as the strike price goes up. This can be explained by the fact that when the prices of underlying commodities go down, that usually means the supply is good, which is akin to good performances by corporates in equity markets.