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Particle-image velocimetry (PIV) has been used in an engine to produce a virtually continuous two-dimensional velocity-vector map over a 12 × 32 mm area. The particle-seeded flow field in the clearance volume of a motored engine (600 r/min, 8:1 compression) was illuminated by a double-pulsed sheet of laser light (20-40μs pulse separation) oriented parallel to the piston. The illuminated particles (<1μm) were photographed at 78deg BTDC compression and 12deg ATDC with 1 × magnification, resulting in paired particle images separated by distances ∼200μm. The two-dimensional velocity distribution was determined by interrogating 0.9-mm square spots on a 0.5-mm grid spacing. The average particle image-pair displacement within each interrogation spot was determined by performing a spatial correlation, and thus the magnitude and direction of the average velocity within the interrogation spot was inferred from the light-pulse separation.