The company said that preliminary studies are underway for the expansion project, which is planned to be completed by 2020.
Press Trust of India cited Indian Oil senior official as saying: "We will get a firm fix on the numbers once studies are completed."
Capable of processing indigenous and imported crude oil, the Panipat refinery commenced operations in 1998 and its capacity was raised to 15MT by 2010.
The latest expansion will allow the complex to meet fuel needs in northwest India.
"We are working on raising fuel quality specifications to meet Euro-IV and V standards at our refineries and so the Panipat expansion too is being reconfigured to meet the new specifications," the official added.
The company plans to increase the capacity of Koyali refinery in Gujarat by 4.3MT from the current 13.7MT a year.
The capacities of Haldia refinery in West Bengal and Mathura refinery in Uttar Pradesh will also be increased to by 0.5MT and 3MT, respectively.
Indian Oil has recently commissioned a refinery at Paradip in the state of Odisha, which complements its existing eight refineries in the country.
