Introductory technical guidance for professional engineers interested in inspection of oil-filled electric power transformers. Here is what is discussed: 1. INTRODUCTION, 2. TRANSFORMER TANK, 3. TOP OIL THERMOMETERS, 4. WINDING TEMPERATURE THERMOMETERS, 5. OIL LEVEL INDICATORS, 6. PRESSURE RELIEF DEVICES, 7. SUDDEN PRESSURE RELAY, 8. BUCHHOLZ RELAY, 9. TRANSFORMER BUSHINGS: TESTING AND MAINTENANCE OF HIGH-VOLTAGE BUSHINGS, 10. OIL PRESERVATION SEALING SYSTEMS, 11. AUXILIARY TANK SEALING SYSTEM.