The study looked at the relationship between the prices of two important types of crude oil, WTI and Brent, from June 1987 to July 2021. Using a periodogram-based method, the researchers found a long-term connection between the prices until the Deepwater Horizon oil spill in 2010. After the spill, this relationship broke down, suggesting that the two oil prices could no longer be used for hedging purposes. The study also identified significant common patterns in both prices before the oil spill.