Abstract. For a cocycle of invertible real n-by-n matrices, the Multiplicative Ergodic Theorem gives an Oseledets subspace decomposition of R n ; that is, above each point in the base space, R n is written as a direct sum of equivariant subspaces, one for each Lyapunov exponent of the cocycle. It is natural to ask if these summands may be further decomposed into equivariant subspaces; that is, if the Oseledets subspaces are reducible. We prove a theorem yielding sufficient conditions for irreducibility of the trivial equivariant subspaces R 2 and C 2 for O 2 (R)-valued cocycles and give explicit examples where the conditions are satisfied.