A coupled pair of O(2)-equivariant bifurcation equations ate developed to model steady axisymmetric Navier-Stokes flow between two concentric cylinders. The flow is driven by the rotation of the inner cylinder and axially periodic boundary conditions are applied at the two end surfaces. We examine the stabilities of steady axisymmetric flows and determine how these stabilities change upon varying the geometric parameters in the model. Our abstract bifurcation equations axe of degree ¡ and are dependent upon three physical paxameters. By considering unfoldings about degenerate singularities we reproduce the qualitative behaviour generated numericaUy by Tavener aad Cliffe [18]. New bifurcation diagrams are produced by varying a parameter held constant by these authors.Key words: Taylor vortex, bifurcation from double eigenvalue, degenerate singularity w IntroductionIn this paper we perform a mathematical analysis of steady, axisymmetric Navier-Stokes flows between a pair of concentric cylinders in which the flow is driven by the rotation of the inner cyUnder alone. In the physical experiment, both the outer cylinder and top and bottom surfaces are stationary and for smaU Reynolds numbers, (the dimensionless angular velocity of the inner cylinder), there is a unique steady flow in which the particle paths ate essentiaUy circular except near the top and bottom surfaces. This flow loses stability with respect to axisymmetric disturbances above a critical Reynolds number. With a gradual increase in the Reynolds number an axisymmetric steady flow develops, comprising a discrete number of toroidal shaped Taylor cells in which the particle paths ate spirals around the in_ ner cylinder. The cellular flow which develops on gradual increase of the Reynolds number is caUed the 'primary' flow. Taylor cells prefer to have ah approximately square cross-section, hence for cylinders with length to gap width ratios near two, the stable primary flow is a two-cell flow. For cylinders with length to gap width ratios near four, the stable primary flow is a four-cell flow. Except in very short cylinders, the primary flow is always observed to have even number of ceUs. We wish to understand how the change from a two-cell primary flow to a four-cell primary flow occurs with increasing length to gap width ratio. We relax the physical boundary conditions and apply axially periodic boundary conditions (as opposed to nonslip conditions) at the two ends. With these boundary conditions, a purely axThe ¡ author is partially supported by Ohbayashi Corporation.