Gas-solid fluidization relies on selecting appropriate operating regimes as the first and foremost consideration for diverse applications. Among different fluidization modes, the proposal of fast fluidization has long been debated. The two epoch-making applications, circulating fluidized bed combustors (CFBC) and fluid catalytic cracking (FCC) risers, are traditionally regarded as fast fluidized beds. The hydrodynamics in CFBC was described as the superposition of a bubbling bed in the bottom region and an entrained bed in the upper region as we previously reported (Fuel, 2021). This study suggests conventional FCC risers operate as a circulating turbulent fluidized bed in the bottom-section with pneumatic solids transport in the upper-section, through investigation into hydrodynamics and oil conversions in the reactor. Without these two foundational operations, fast fluidization regime appears to lack industrial applicability and may be better regarded as a theoretical extension bridging bubbling and turbulent fluidization.