We present spatially resolved measurements characterizing the stagnation layer between two obliquely merging supersonic plasma jets. Intra-jet collisionality is very high (λii ≪ 1 mm), but the inter-jet ion-ion mean free paths are on the same order as the stagnation layer thickness (a few cm). Fast-framing camera images show a double-peaked emission profile transverse to the stagnation layer, with the central emission dip consistent with a density dip observed in the interferometer data. We demonstrate that our observations are consistent with collisional oblique shocks.Colliding plasmas have been studied in a variety of contexts, e.g., counterstreaming laser-produced plasmas supporting hohlraum design for indirect-drive inertial confinement fusion [1][2][3], forming and studying astrophysically relevant shocks [4][5][6][7][8], and for applications such as pulsed laser deposition [9] and laser-induced breakdown spectroscopy [10]. Physics issues arising in these studies include plasma interpenetration [11][12][13][14][15][16], shock formation [17], and the formation and dynamics of a stagnation layer [18][19][20]. In this work, we present experimental results on two obliquely merging supersonic plasma jets, which are in a different and more collisional parameter regime than many of the colliding plasma examples mentioned above. Ours and other recent jet-merging experiments [21,22] were conducted to explore the feasibility of forming imploding spherical plasma liners via an array of merging plasma jets [23][24][25][26][27], which could have applications in forming cm-, µs-, and Mbar-scale plasmas for fundamental high-energy-density-physics studies [28] and as a standoff driver for magnetoinertial fusion [23,[29][30][31][32]. Prior experiments studying the stagnation layer between colliding laser-produced or wire-array z-pinch [33] plasmas were on smaller spatial scales (mm or smaller) that could not be fully resolved by measurements. New results in the present work are the experimental identification and characterization of a few-cm thick stagnation layer between colliding plasmas, and the demonstration that our observations are consistent with hydrodynamic oblique shock theory [34].Experiments reported here are conducted on the Plasma Liner Experiment (PLX) [35], in which two supersonic argon plasma jets are formed and launched by plasma railguns [36]. Plasma jet parameters at the exit of the railgun nozzle (peak n e ≈ 2 × 10 16 cm −3 , peak T e ≈ 1.4 eV, V jet ≈ 30 km/s, Mach number M ≡ V jet /C s,jet ≈ 14, diameter = 5 cm, and length ≈ 20 cm) and their evolution during subsequent jet propagation have been characterized in detail [35]. The jet magnetic field inside the railgun is ∼3 T, but the classical magnetic diffusion time is a few µs [35], and thus • apart, two merging plasma jets, R-Z coordinates used in the paper, approximate interferometer/spectrometer linesof-sight (Z ≈ 84 cm), and CCD camera field-of-view.we ignore the effects of a magnetic field by the time of jet merging (> 20 µs). Experimental data ...