In the event of a pipeline or vessel leak or rupture at an oil and gas production facility, understanding of vapor-liquid multiphase flows can be very helpful in mitigating the safety and environmental consequences. The relevant multiphase flow phenomena involve flows both internal and external to the pipe or vessel. They include the release rates of vapor and liquid hydrocarbons, the sonic flow region immediately downstream of the opening, possible generation of aerosols, and possible segregation of the efflux into a gas jet and a liquid pool. If the release does not ignite, it is important to be able to describe the dispersion of the heavy multiphase plume. If the release does ignite, the size, position, and luminosity of the resulting jet and pool fires are important. Many aspects of these flow phenomena are not well understood. A survey is made of the relevant issues, existing calculation methods, and suggested research initiatives.