The study analyzes the effect of speculative bubbles in oil prices on cryptocurrency returns, with special attention to the heterogeneity among clean and dirty cryptocurrencies. The DS-LPPLS model is employed to detect positive and negative bubble episodes in WTI oil prices. Findings obtained from daily data collected from July 2018 to June 2025 show that oil prices exhibited both negative and positive bubble characteristics and that these price bubbles significantly increased cryptocurrency returns, with negative bubble periods having the strongest effects. Regarding the consensus mechanism, the results reveal that clean cryptocurrencies benefit consistently from oil price bubbles, implying that they could serve as a green hedge during negative bubbles. On the contrary, dirty cryptocurrencies respond more strongly to negative bubbles, owing to their reliance on energy-intensive mining processes. These findings offer fresh perspectives on the relationship between energy and cryptocurrency markets, with significant implications for investors, policymakers, and sustainable finance debates.