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The 56 tonne high resolution liquid scintillation calorimeter KARMEN at the beam stop neutrino source ISIS has been used to search for neutrino oscillations in the disappearance channel νe→ νx . The νe emitted in µ + decay at rest are detected with spectroscopic quality via the exclusive charged current reaction 12 C ( νe , e − ) 12 Ng.s. almost free of background. Analysis of the spectral shape of e − from the νe-induced reaction as well as a measurement of the absolute νe flux allow to investigate oscillations of the type νe→ ντ and νe→ νµ. The flux independent ratio R CC/NC of charged current events 12 C ( νe , e − ) 12 Ng.s. to neutral current events 12 C ( ν , ν ′ ) 12 C * provides additional information in the oscillation channel νe→ νx. All three analysis methods show no evidence for oscillations. For the νe→ ντ channel 90% CL limits of sin 2 (2Θ) < 0.338 for ∆m 2 ≥ 100 eV 2 /c 4 and ∆m 2 < 0.77 eV 2 /c 4 for maximal mixing in a simple 2 flavor oscillation formalism are derived. A complete 3 flavor analysis of the experimental data from five years of measurement with respect to νe↔ ντ and νe↔ νµ mixing is presented.