High-resolution particle image velocimetry measurements were performed on laminar and transitional oblique shock wave reflections for a range of Mach numbers ( $M=1.6{-}2.3$ ), Reynolds numbers ( $Re_{x_{sh}}=1.4\times 10^{6}{-}3.5\times 10^{6}$ ) and flow deflection angles ( $\unicode[STIX]{x1D703}=1^{\circ }{-}5^{\circ }$ or $p_{3}/p_{1}=1.11{-}1.64$ ). The laminar interactions revealed a long, flat and triangular shaped separation bubble. For relatively strong interactions ( $p_{3}/p_{1}>1.2$ ), the bubble grows linearly in the upstream direction with increasing shock strength. Under these conditions, the boundary layer keeps an on average laminar velocity profile up to the shock impingement location, followed by a quick transition and subsequent reattachment of the boundary layer. For weaker interactions ( $p_{3}/p_{1}<1.2$ ), the boundary layer is able to remain laminar further downstream of the bubble, which consequently results in a later reattachment of the boundary layer. The pressure distribution at the interaction onset for all laminar cases shows excellent agreement with the free-interaction theory, therefore supporting its validity even for incipiently separated laminar oblique shock wave reflections.