STOMP subsurface transport over multiple phases. Subsurface Transport Over Multiple Phases (STOMP) is a sequential numerical simulator for modeling multifluid flow and transport through geologic media. Written in ANSI Standard FORTRAN, STOMP has been executed on a variety of platforms at national laboratories, government agencies, private companies, and universities. STOMP-SC is a scalable, parallel scientific computer code, which, like STOMP, comprises a collection of operational modes for modeling subsurface flow and reactive transport and is being implemented on the massively parallel computers at the Environmental Molecular Science Laboratory. STOMP-SC is currently under development, offering a subset of the STOMP operational modes and process modeling capabilities. The STOMP and STOMP-SC simulators are currently being used nationally and internationally at research laboratories and universities. Certain versions of STOMP are available for distribution, while others are restricted to research use only. A general summary of capabilities is shown below. See Operational Modes for a more detailed description of specific capabilities.