  We report an experimental study of the spontaneous spatial and temporal
coherence of polariton condensates generated in the optical parametric
oscillator configuration, below and at the parametric threshold, and as a
function of condensate area. Above the threshold we obtain very long coherence
times (up to 3 ns) and a spatial coherence extending over the entire condensate
(40 \mu m). The very long coherence time and its dependence on condensate area
and pump power reflect the suppression of polariton-polariton interactions by
an effect equivalent to motional narrowing.
