E-Plus is a device that purportedly increases the fuel efficiency of internal-combustion engines by modifying the intaken air, so that more oxygen is available for combustion. The electrical device uses computer circuitry and a "cold-plasma partial-discharge process", and it is claimed that fuel savings of 10-20% are regularly achieved and that the device can be used with most car engines.

E-Plus was invented by Dr Birasak Varasundharosoth from Thailand; the patent was filed in late 2003.

The device is already for sale in Thailand, at a price of less than US$100 per unit. Its lifetime is estimated to be 4 years.