  After reviewing the calculation of the Standard Model one-loop effective
potential in a class of linear gauges, we discuss the physical observables
entering the vacuum stability analysis. While the electroweak-vacuum-stability
bound on the Higgs boson mass can be formally proven to be gauge independent,
the field value at which the effective potential turns negative (the so-called
instability scale) is a gauge dependent quantity. By varying the gauge-fixing
scheme and the gauge-fixing parameters in their perturbative domain, we find an
irreducible theoretical uncertainty of at least two orders of magnitude on the
scale at which the Standard Model vacuum becomes unstable.
