  We present a path integral Monte Carlo method which is the full quantum
analogue of the Gibbs ensemble Monte Carlo method of Panagiotopoulos to study
the gas-liquid coexistence line of a classical fluid. Unlike previous
extensions of Gibbs ensemble Monte Carlo to include quantum effects, our scheme
is viable even for systems with strong quantum delocalization in the degenerate
regime of temperature. This is demonstrated by an illustrative application to
the gas-superfluid transition of $^4$He in two dimensions.
