How to produce exotic matter using classical fields

The field equations and energy-momentum tensor are derived for a charged ideal fluid coupled to a scalar field. It is shown that there exists an interaction energy-momentum tensor which can have negative energy densities even though the fluid and fields have positive energy densities. The energy density and mass of a fluid sphere are calculated in the weak field limit and it is shown that they can be negative if certain conditions are met. When the mass of the sphere is negative the entire interior consists of exotic matter (i.e., matter which violates the weak energy condition).