This chapter examines the financialisation of oil markets and its profound impact on global commodity trading, culminating in the events leading to and following the 2008 Great Recession. It traces how increased market transparency, the rise of derivative products, and the influx of hedge funds, pension funds, and institutional investors transformed oil from a physically driven commodity to a heavily traded financial asset. Through mechanisms like index products, ETFs, and structured notes, banks, and financial institutions facilitated unprecedented investor access, driving price volatility and disconnecting oil prices from traditional supply–demand fundamentals. The chapter explores how these dynamics contributed to the dramatic price spike and collapse in 2008, while analysing debates over the roles of speculation versus market fundamentals. It also delves into the regulatory aftermath—highlighting reforms like the Volcker Rule and Dodd-Frank Act—which triggered the retreat of Wall Street banks from physical commodity trading, leaving the field open for independent traders. Ultimately, the chapter underscores how financialisation reshaped oil markets, influencing trading strategies, risk management practices, and regulatory landscapes.