The linear stability properties of collisionless drift instabilities are analyzed in a Harris equilibrium model B0xtanh(z/L) of the plasma sheet boundary layer (PSBL). The streaming ions with drift type instabilities driven by v0∥(z)≂v(z) in the PSBL are considered. The fluid approximation leads to growth from ∂T/∂z and ∂v0∥/∂z but predicts that the mode width Δz approaches the gyroradius &rgr;i of the energetic ions. Thus an integral equation theory for the modes is developed taking into account that in the PSBL the curvature drift is weak compared with the grad-B drift vDB. The exact wave particle resonance &ohgr;=kxvx+kyvDB(v⊥2) is kept in the nonlocal response functions. Plasma density, temperature, and magnetic gradient drift motions are taken into account. The drift modes driven by ∂vx/∂z reduce an anomalous cross-field momentum transport mixing the PSBL ions on the time scale of tens of seconds. A nonlinear simulation is performed which shows the coalescence of the small scale, fast growing modes into large-scale vortices. The relation between these collective modes and plasma sheet transport phenomena is discussed including the comparison with the competing plasma mixing from single-particle stochasticity. ¿ American Geophysical Union 1993