The traditional way is to invest in large oil producers (XOM, BP, etc.), whose stocks are pretty strongly correlated with oil prices. But that's also placing a secondary bet that they won't go bankrupt before oil goes back up.
There are also ETFs that try to directly proxy oil prices by holding and continually rolling over near-dated oil futures. USO is the biggest of those. They have some technical issues tracking oil prices though, especially for long-term buy-and-hold strategies: https://www.investopedia.com/articles/markets/081116/uso-goo...
There are also ETFs that try to directly proxy oil prices by holding and continually rolling over near-dated oil futures. USO is the biggest of those. They have some technical issues tracking oil prices though, especially for long-term buy-and-hold strategies: https://www.investopedia.com/articles/markets/081116/uso-goo...