The description of the compressible gas flow in the throat region of unconventional rocket nozzles must be known in order to optimize the wall contours and to predict the performance. The existence of both subsonic and supersonic flow in close proximity does not permit the use of conventional analytical techniques to obtain a mathematical description of the flow. The analysis presented in this paper can treat annular flow passages that are either parallel to the nozzle axis or inclined to it at some arbitrary angle. The solution is not limited to nozzles with moderate wall radii of curvature; sufficient terms have been retained in the series solution to treat nearly sharp wall curvatures in the throat region. The usual assumption of steady, isentropic, irrotational flow with constant specific heats is made. The shape of the sonic line is not symmetrical about the geometric center of the annular throat as in the case of bell nozzles. The flow reaches sonic velocity further upstream of the geometric throat on the inner wall than on the outer wall, wall curvatures being equal.