Arendt, W.Sourour, A. R.2010-05-102010-05-1019852010-05-10http://hdl.handle.net/1828/2738For regular operators on a Banach lattice, we introduce and investigate two notions of order essential spectrum analogous to the essential spectrum and the Weyl spectrum for operators on Banach spaces. We also discuss related questions on the behaviour of the order spectrum under perturbation by r-compact operators.entechnical reports (mathematics and statistics)Perturbation of regular operators and the order essential spectrumTechnical ReportDepartment of MathematicsDepartment of Mathematics and Statistics