Which companies are major transformer oil manufacturers in India?

Major manufacturers and suppliers in India are typically those who produce or distribute mineral insulating oils and ester fluids that meet IS 335 or IEC aligned specifications and appear on utility qualified vendor lists. Examples often cited in the market include Apar Industries and Savita Oil Technologies. However, the correct answer for an engineering context is vendor specific: it depends on oil type, inhibited or uninhibited formulation, required testing certificates, and your end user qualification process. Many utilities also buy through approved distributors tied to batch testing and traceability requirements.