The study investigates the size and shape determination of nucleoli in Xenopus laevis oocytes, focusing on their liquid-like behavior. Nucleoli exhibit characteristic viscous fluid dynamics, behaving as liquid-like droplets of RNA and protein. This behavior is ATP-dependent, suggesting active processes in fluidizing internal contents. Nucleoli restructure into spherical droplets under mechanical deformations due to their surface tension and fluidity. The nucleoli show a broad distribution of sizes with a power-law distribution, which is attributed to spontaneous coalescence events. These findings provide insights into the function of nucleoli in ribosome subunit processing and link molecular activities within macromolecular assemblies to their physical properties. The study also highlights the role of ATP in maintaining nucleolar liquidity and the potential significance of nucleolar fusion in cell growth and malignancy.The study investigates the size and shape determination of nucleoli in Xenopus laevis oocytes, focusing on their liquid-like behavior. Nucleoli exhibit characteristic viscous fluid dynamics, behaving as liquid-like droplets of RNA and protein. This behavior is ATP-dependent, suggesting active processes in fluidizing internal contents. Nucleoli restructure into spherical droplets under mechanical deformations due to their surface tension and fluidity. The nucleoli show a broad distribution of sizes with a power-law distribution, which is attributed to spontaneous coalescence events. These findings provide insights into the function of nucleoli in ribosome subunit processing and link molecular activities within macromolecular assemblies to their physical properties. The study also highlights the role of ATP in maintaining nucleolar liquidity and the potential significance of nucleolar fusion in cell growth and malignancy.