  We use the two loop effective potential to study the first order electroweak
phase transition in the minimial supersymmetric standard model. A global search
of the parameter space is made to identify parameters compatible with
electroweak baryogenesis. We improve on previous such studies by fully
incorporating squark and Higgs boson mixing, by using the latest experimental
constraints, and by computing the latent heat and the sphaleron rate. We find
the constraints tan beta > 2.1, top squark mass < 172 GeV, and Higgs mass < 107
GeV (becoming more or less restrictive if the heavy stop has mass less than or
greater than 1 TeV). We also find that the change in tan beta in the bubble
wall is rarely greater than 0.001, which severely constrains the mechanism of
baryogenesis.
