multiUQ: an intrusive uncertainty quantification tool for gas-liquid multiphase flows. Uncertainty quantification (UQ) of fluid flows offers the ability to understand the impact of variation in fluid properties, boundary conditions, and initial conditions on simulation results. In this work, an open-source program called multiUQ is developed which performs UQ using an intrusive approach applied to gas-liquid multiphase flows. Intrusive methods require modifying the governing equations by incorporating stochastic (uncertain) variables. This adds complexity but reduces computational cost compared to non-intrusive methods (e.g. Monte Carlo). To date, much of the work on intrusive UQ has focused on single phase flows. We extend this work by adding capabilities for gas-liquid flows which include a stochastic conservative level set method to capture the location of the phase interface, computing a stochastic curvature, and development of a stochastic surface tension force. Several test cases are presented which illustrate the strength of the framework. Both deterministic and stochastic channel flow cases converge to analytic results and demonstrate the accuracy of the level set transport. Zalesak’s disk and the deformation test cases further highlight the abilities of the transport method as well as the robustness of the reinitialization equation, which maintains the level set profile. Deterministic and stochastic oscillating droplet test cases paired with analytic results, solve a true multiphase flow problem, and highlight the abilities of the UQ framework. Finally, results from a stochastic atomizing jet show droplet breakup and merging for cases of uncertainty about the surface tension coefficient and incoming velocity.